Publications

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• Differential Shannon Entropies and Mutual Information in a Curve Crossing System: Adiabatic and Diabatic Decompositions. Schürger, P.; Engel, V. In Journal of Chemical Theory and Computation, 20(12), S. 5012–5021. American Chemical Society (ACS), 2024.
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  @article{Schuerger_2024, author = {Schürger, P. and Engel, V.}, journal = {Journal of Chemical Theory and Computation}, keywords = {newest}, month = {06}, number = 12, pages = {5012–5021}, publisher = {American Chemical Society (ACS)}, title = {Differential Shannon Entropies and Mutual Information in a Curve Crossing System: Adiabatic and Diabatic Decompositions}, volume = 20, year = 2024 }

• Differential Shannon entropies and correlation measures for Born–Oppenheimer electron–nuclear dynamics: numerical results and their analytical interpretation. Schürger, Peter; Engel, Volker. In Phys. Chem. Chem. Phys., 25(41), S. 28373–28381. The Royal Society of Chemistry, 2023.
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  @article{D3CP03573E, author = {Schürger, Peter and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {newest}, number = 41, pages = {28373-28381}, publisher = {The Royal Society of Chemistry}, title = {Differential Shannon entropies and correlation measures for Born–Oppenheimer electron–nuclear dynamics: numerical results and their analytical interpretation}, volume = 25, year = 2023 }
• Information Theoretical Approach to Coupled Electron-Nuclear Wave Packet Dynamics: Time-Dependent Differential Shannon Entropies. Schürger, Peter; Engel, Volker. In The Journal of Physical Chemistry Letters, 14(2), S. 334–339. American Chemical Society ({ACS}), 2023.
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  @article{Schuerger_2023, author = {Schürger, Peter and Engel, Volker}, journal = {The Journal of Physical Chemistry Letters}, keywords = {newest}, month = {01}, number = 2, pages = {334–339}, publisher = {American Chemical Society ({ACS})}, title = {Information Theoretical Approach to Coupled Electron-Nuclear Wave Packet Dynamics: Time-Dependent Differential Shannon Entropies}, volume = 14, year = 2023 }
• On the relation between nodal structures in quantum wave functions and particle correlation. Schürger, Peter; Engel, Volker. In AIP Advances, 13(12). AIP Publishing, 2023.
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  @article{Schrger_nodes, author = {Schürger, Peter and Engel, Volker}, journal = {AIP Advances}, keywords = {newest}, month = 12, number = 12, publisher = {AIP Publishing}, title = {On the relation between nodal structures in quantum wave functions and particle correlation}, volume = 13, year = 2023 }
• Differential Shannon Entropies Characterizing Electron-Nuclear Dynamics and Correlation: Momentum-Space Versus Coordinate-Space Wave Packet Motion. Schürger, Peter; Engel, Volker. In Entropy, 25(7), S. 970. {MDPI} {AG}, 2023.
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  @article{Sch_rger_2023, author = {Schürger, Peter and Engel, Volker}, journal = {Entropy}, keywords = {newest}, month = {06}, number = 7, pages = 970, publisher = {{MDPI} {AG}}, title = {Differential Shannon Entropies Characterizing Electron-Nuclear Dynamics and Correlation: Momentum-Space Versus Coordinate-Space Wave Packet Motion}, volume = 25, year = 2023 }

• Nuclear-Electron Correlation Effects and Their Photoelectron Imprint in Molecular XUV Ionisation. Ziems, Karl Michael; Bruhnke, Jakob; Engel, Volker; Gräfe, Stefanie. In Frontiers in Chemistry, 10. Frontiers Media {SA}, 2022.
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  @article{Ziems_2022, author = {Ziems, Karl Michael and Bruhnke, Jakob and Engel, Volker and Gräfe, Stefanie}, journal = {Frontiers in Chemistry}, keywords = {grk2112}, month = {08}, publisher = {Frontiers Media {SA}}, title = {Nuclear-Electron Correlation Effects and Their Photoelectron Imprint in Molecular XUV Ionisation}, volume = 10, year = 2022 }
• Third-order pump-probe spectroscopy applied to molecular dimers: Characterization of relaxation dynamics and exciton--exciton annihilation. Glaab, Fabian; Süß, Jasmin; Engel, Volker. In Phys. Chem. Chem. Phys., 24(41), S. 25316–25326. The Royal Society of Chemistry, 2022.
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  @article{D2CP03435B, abstract = {We investigate theoretically the excitonic dynamics in molecular dimers which is monitored by two time-delayed femtosecond laser pulses. A two-photon absorption leads to a wave packet dynamics in the manifold of second excited states. This opens up the channel for exciton–exciton annihilation (EEA) which involves non-radiative electronic transitions. It is shown that the time interval during which EEA takes place can be monitored by the detection of third-order signals which can be interpreted as originating from a pump-probe scheme. In the case of transient absorption{,} the spectra directly map intraband relaxation processes.}, author = {Glaab, Fabian and Süß, Jasmin and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {for1809}, number = 41, pages = {25316–25326}, publisher = {The Royal Society of Chemistry}, title = {Third-order pump-probe spectroscopy applied to molecular dimers: Characterization of relaxation dynamics and exciton–exciton annihilation}, volume = 24, year = 2022 }
• Excitation localization in a trimeric perylenediimide macrocycle: Synthesis, theory, and single molecule spectroscopy. Hauschildt, Simon J.; Wu, Zehua; Uersfeld, Daniel; Schmid, Paul; Götz, Christian; Engel, Volker; Engels, Bernd; Müllen, Klaus; Basch{{é}}, Thomas. In The Journal of Chemical Physics, 156(4), S. 044304. {AIP} Publishing, 2022.
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  @article{Hauschildt_2022, author = {Hauschildt, Simon J. and Wu, Zehua and Uersfeld, Daniel and Schmid, Paul and Götz, Christian and Engel, Volker and Engels, Bernd and Müllen, Klaus and Basch{\'{e}}, Thomas}, journal = {The Journal of Chemical Physics}, keywords = {for1809}, month = {01}, number = 4, pages = {044304}, publisher = {{AIP} Publishing}, title = {Excitation localization in a trimeric perylenediimide macrocycle: Synthesis, theory, and single molecule spectroscopy}, volume = 156, year = 2022 }
• Quantum flux densities for electronic-nuclear motion: exact versus Born-Oppenheimer dynamics. Schaupp, Thomas; Engel, Volker. In Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 380(2223), S. 25316–25326. The Royal Society, 2022.
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  @article{Schaupp_2022, author = {Schaupp, Thomas and Engel, Volker}, journal = {Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences}, keywords = {for1809}, month = {03}, number = 2223, pages = {25316 - 25326}, publisher = {The Royal Society}, title = {Quantum flux densities for electronic-nuclear motion: exact versus Born-Oppenheimer dynamics}, volume = 380, year = 2022 }
• Correlated three-dimensional electron-nuclear motion: Adiabatic dynamics vs passage of conical intersections. Schaupp, Thomas; Engel, Volker. In The Journal of Chemical Physics, 156(7), S. 074302. {AIP} Publishing, 2022.
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  @article{Schaupp_2022, author = {Schaupp, Thomas and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {grk2112}, month = {02}, number = 7, pages = {074302}, publisher = {{AIP} Publishing}, title = {Correlated three-dimensional electron-nuclear motion: Adiabatic dynamics vs passage of conical intersections}, volume = 156, year = 2022 }
• Time-Dependent Expectation Values from Integral Equations for Quantum Flux and Probability Densities. Schürger, P.; Renziehausen, K.; Schaupp, T.; Barth, I.; Engel, V. In The Journal of Physical Chemistry A, 126(48), S. 8964–8975. American Chemical Society ({ACS}), 2022.
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  @article{Sch_rger_2022, author = {Schürger, P. and Renziehausen, K. and Schaupp, T. and Barth, I. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {newest}, month = 11, number = 48, pages = {8964–8975}, publisher = {American Chemical Society ({ACS})}, title = {Time-Dependent Expectation Values from Integral Equations for Quantum Flux and Probability Densities}, volume = 126, year = 2022 }
• Wave packet dynamics in an harmonic potential disturbed by disorder: Entropy, uncertainty, and vibrational revivals. Schürger, Peter; Schaupp, Thomas; Kaiser, Dustin; Engels, Bernd; Engel, Volker. In The Journal of Chemical Physics, 156(5), S. 054303. {AIP} Publishing, 2022.
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  @article{Schuerger_2022, author = {Schürger, Peter and Schaupp, Thomas and Kaiser, Dustin and Engels, Bernd and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {for1809}, month = {02}, number = 5, pages = {054303}, publisher = {{AIP} Publishing}, title = {Wave packet dynamics in an harmonic potential disturbed by disorder: Entropy, uncertainty, and vibrational revivals}, volume = 156, year = 2022 }

• Time-dependent momentum expectation values from different quantum probability and flux densities. Schaupp, Thomas; Renziehausen, Klaus; Barth, Ingo; Engel, Volker. In The Journal of Chemical Physics, 154(6), S. 064307. {AIP} Publishing, 2021.
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  @article{Schaupp_2021, author = {Schaupp, Thomas and Renziehausen, Klaus and Barth, Ingo and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {02}, number = 6, pages = {064307}, publisher = {{AIP} Publishing}, title = {Time-dependent momentum expectation values from different quantum probability and flux densities}, volume = 154, year = 2021 }
• Twisting versus Delocalization in CAAC- and NHC-Stabilized Boron-Based Biradicals: The Roles of Sterics and Electronics. Schmid, Paul; Fantuzzi, Felipe; Klopf, Jonas; Schröder, Niklas B.; Dewhurst, Rian D.; Braunschweig, Holger; Engel, Volker; Engels, Bernd. In Chemistry – A European Journal, 27(16), S. 5160–5170. Wiley, 2021.
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  @article{Schmid_2021, author = {Schmid, Paul and Fantuzzi, Felipe and Klopf, Jonas and Schröder, Niklas B. and Dewhurst, Rian D. and Braunschweig, Holger and Engel, Volker and Engels, Bernd}, journal = {Chemistry – A European Journal}, keywords = {ak-engel}, month = {01}, number = 16, pages = {5160–5170}, publisher = {Wiley}, title = {Twisting versus Delocalization in CAAC- and NHC-Stabilized Boron-Based Biradicals: The Roles of Sterics and Electronics}, volume = 27, year = 2021 }
• Optically Induced Charge Transfer in Organic Mixed-Valence Systems: Wave Packet Dynamics and Femtosecond Transient Spectroscopy. Glaab, F.; Lambert, C.; Engel, V. In The Journal of Physical Chemistry A, 125(19), S. 4114–4125. American Chemical Society ({ACS}), 2021.
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  @article{Glaab_2021, abstract = {We theoretically study the dynamics of charge transfer induced by femtosecond laser-pulse excitation. Models involving coupled electronic states of symmetrically bridged organic mixed-valence molecules are investigated, where the motion proceeds along two reaction coordinates. Linear absorption spectra of two species that differ in the energetical position of the bridge, relative to acceptor and donor states, are determined and compared to experimental results. From the wave packet dynamics it emerges that relaxation dominates the charge transfer. This behavior is reflected in transient absorption spectra, which are obtained from a directional decomposition of the time-dependent polarization. Due to the nature of the coupled dynamics the extraction of the relevant contributions needs an extension of well-known techniques for the decomposition.}, author = {Glaab, F. and Lambert, C. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {grk2112}, month = {05}, number = 19, pages = {4114–4125}, publisher = {American Chemical Society ({ACS})}, title = {Optically Induced Charge Transfer in Organic Mixed-Valence Systems: Wave Packet Dynamics and Femtosecond Transient Spectroscopy}, volume = 125, year = 2021 }

• Born–Oppenheimer and non-Born–Oppenheimer contributions to time-dependent electron momenta. Schaupp, Thomas; Engel, Volker. In J. Chem. Phys., 152(20), S. 204310. American Institute of Physics, 2020.
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  @article{schaupp2020bornoppenheimer, abstract = {Using a model system for a coupled electron–nuclear motion, we calculate time-dependent expectation values of the electronic momentum operator. Whereas, within the velocity form, this quantity vani...}, author = {Schaupp, Thomas and Engel, Volker}, booktitle = {The Journal of Chemical Physics}, journal = {J. Chem. Phys.}, keywords = {ak-engel}, month = {05}, number = 20, pages = 204310, publisher = {American Institute of Physics}, title = {Born–Oppenheimer and non-Born–Oppenheimer contributions to time-dependent electron momenta}, volume = 152, year = 2020 }
• A wave packet picture of exciton–exciton annihilation: Molecular dimer dynamics. Süß, J; Engel, V. In J. Chem. Phys., 152(17), S. 174305. American Institute of Physics, 2020.
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  @article{suss2020packet, abstract = {The usual view of exciton–exciton annihilation (EEA) processes in molecular aggregates is based on locally excited states of the monomer units. However, the corresponding localized configurations c...}, author = {Süß, J and Engel, V}, booktitle = {The Journal of Chemical Physics}, journal = {J. Chem. Phys.}, keywords = {ak-engel}, month = {05}, number = 17, pages = 174305, publisher = {American Institute of Physics}, title = {A wave packet picture of exciton–exciton annihilation: Molecular dimer dynamics}, volume = 152, year = 2020 }
• Exciton–exciton annihilation in a molecular trimer: Wave packet dynamics and 2D spectroscopy. Süß, J; Engel, V. In J. Chem. Phys., 153(16), S. 164310. American Institute of Physics, 2020.
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  @article{suss2020excitonexciton, abstract = {We theoretically study the exciton–exciton annihilation (EEA) in a molecular trimer MMM. The system is treated within a model of electronic states, and the coupling to a bath is incorporated using the quantum jump method. Two situations of initial excitation are compared. In the first one, a two-photon process populates configurations M*M*M and MM*M* so that two excitons reside on neighboring monomers M. Then, EEA can immediately proceed. In contrast, if the trimer initially is in the local configuration M*MM*, exciton diffusion must occur before the annihilation process can take place. For the trimer, this excitonic motion takes place on a very short time scale. In both cases, wave packets are prepared which show a different quantum dynamics where the latter depends on the couplings and decay rates. It is documented how fifth-order coherent two-dimensional spectroscopy can be used to directly map the EEA as a function of time.}, author = {Süß, J and Engel, V}, booktitle = {The Journal of Chemical Physics}, journal = {J. Chem. Phys.}, keywords = {grk1221}, month = 10, number = 16, pages = 164310, publisher = {American Institute of Physics}, title = {Exciton–exciton annihilation in a molecular trimer: Wave packet dynamics and 2D spectroscopy}, volume = 153, year = 2020 }
• Naphthoquinones as Covalent Reversible Inhibitors of Cysteine Proteases{\textemdash}Studies on Inhibition Mechanism and Kinetics. Klein, Philipp; Barthels, Fabian; Johe, Patrick; Wagner, Annika; Tenzer, Stefan; Distler, Ute; Le, Thien Anh; Schmid, Paul; Engel, Volker; Engels, Bernd; Hellmich, Ute A.; Opatz, Till; Schirmeister, Tanja. In Molecules, 25(9), S. 2064. {MDPI} {AG}, 2020.
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  @article{Klein_2020, author = {Klein, Philipp and Barthels, Fabian and Johe, Patrick and Wagner, Annika and Tenzer, Stefan and Distler, Ute and Le, Thien Anh and Schmid, Paul and Engel, Volker and Engels, Bernd and Hellmich, Ute A. and Opatz, Till and Schirmeister, Tanja}, journal = {Molecules}, keywords = {ak-engel}, month = {04}, number = 9, pages = 2064, publisher = {{MDPI} {AG}}, title = {Naphthoquinones as Covalent Reversible Inhibitors of Cysteine Proteases{\textemdash}Studies on Inhibition Mechanism and Kinetics}, volume = 25, year = 2020 }
• cAAC-Stabilized 9,10-diboraanthracenes—Acenes with Open-Shell Singlet Biradical Ground States. Saalfrank, Christian; Fantuzzi, Felipe; Kupfer, Thomas; Ritschel, Benedikt; Hammond, Kai; Krummenacher, Ivo; Bertermann, Rüdiger; Wirthensohn, Raphael; Finze, Maik; Schmid, Paul; Engel, Volker; Engels, Bernd; Braunschweig, Holger. In Angewandte Chemie International Edition, 59(43), S. 19338–19343. Wiley, 2020.
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  @article{Saalfrank_2020, author = {Saalfrank, Christian and Fantuzzi, Felipe and Kupfer, Thomas and Ritschel, Benedikt and Hammond, Kai and Krummenacher, Ivo and Bertermann, Rüdiger and Wirthensohn, Raphael and Finze, Maik and Schmid, Paul and Engel, Volker and Engels, Bernd and Braunschweig, Holger}, journal = {Angewandte Chemie International Edition}, keywords = {ak-engel}, month = {08}, number = 43, pages = {19338–19343}, publisher = {Wiley}, title = {cAAC-Stabilized 9,10-diboraanthracenes—Acenes with Open-Shell Singlet Biradical Ground States}, volume = 59, year = 2020 }

• Electronic and nuclear flux dynamics at a conical intersection. Schaupp, Thomas; Engel, Volker. In J. Chem. Phys., 151(8), S. 084309. American Institute of Physics, 2019.
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  @article{schaupp2019electronic, abstract = {A combined electronic-nuclear wave packet motion is accompanied by temporal changes of probability flux densities. Using a two dimensional model, we study such densities in the vicinity of a conica...}, author = {Schaupp, Thomas and Engel, Volker}, booktitle = {The Journal of Chemical Physics}, journal = {J. Chem. Phys.}, keywords = {ak-engel}, month = {08}, number = 8, pages = {084309}, publisher = {American Institute of Physics}, title = {Electronic and nuclear flux dynamics at a conical intersection}, volume = 151, year = 2019 }
• Optically Induced Electron Transfer in Mixed-Valence States: A Model Study on Electronic Transitions, Relaxation Dynamics, and Transient Absorption Spectroscopy. Glaab, Fabian; Wehner, Johannes G.; Lambert, Christoph; Engel, Volker. In J. Phys. Chem. A, 123, S. 5463–5471. 2019.
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  @article{noauthororeditor, author = {Glaab, Fabian and Wehner, Johannes G. and Lambert, Christoph and Engel, Volker}, journal = {J. Phys. Chem. A}, keywords = {for1809}, pages = {5463-5471}, title = {Optically Induced Electron Transfer in Mixed-Valence States: A Model Study on Electronic Transitions, Relaxation Dynamics, and Transient Absorption Spectroscopy}, volume = 123, year = 2019 }
• Mapping of exciton–exciton annihilation in a molecular dimer via fifth-order femtosecond two-dimensional spectroscopy. Süß, J; Wehner, J; Dostál, J; Brixner, T; Engel, V. In J. Chem. Phys., 150(10), S. 104304. American Institute of Physics, 2019.
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  @article{suss2019mapping, abstract = {We present a theoretical study on exciton–exciton annihilation (EEA) in a molecular dimer. This process is monitored using a fifth-order coherent two-dimensional (2D) spectroscopy as was recently proposed by Dostál et al. [Nat. Commun. 9, 2466 (2018)]. Using an electronic three-level system for each monomer, we analyze the different paths which contribute to the 2D spectrum. The spectrum is determined by two entangled relaxation processes, namely, the EEA and the direct relaxation of higher lying excited states. It is shown that the change of the spectrum as a function of a pulse delay can be linked directly to the presence of the EEA process.}, author = {Süß, J and Wehner, J and Dostál, J and Brixner, T and Engel, V}, booktitle = {The Journal of Chemical Physics}, journal = {J. Chem. Phys.}, keywords = {for1809}, month = {03}, number = 10, pages = 104304, publisher = {American Institute of Physics}, title = {Mapping of exciton–exciton annihilation in a molecular dimer via fifth-order femtosecond two-dimensional spectroscopy}, volume = 150, year = 2019 }
• Lewis-Base Stabilization of the Parent Al(I) Hydride under Ambient Conditions. Mellerup, Soren K.; Cui, Yunshu; Fantuzzi, Felipe; Schmid, Paul; Goettel, James T.; Bélanger-Chabot, Guillaume; Arrowsmith, Merle; Krummenacher, Ivo; Ye, Qing; Engel, Volker; Engels, Bernd; Braunschweig, Holger. In Journal of the American Chemical Society, 141(42), S. 16954–16960. American Chemical Society (ACS), 2019.
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  @article{Mellerup_2019, author = {Mellerup, Soren K. and Cui, Yunshu and Fantuzzi, Felipe and Schmid, Paul and Goettel, James T. and Bélanger-Chabot, Guillaume and Arrowsmith, Merle and Krummenacher, Ivo and Ye, Qing and Engel, Volker and Engels, Bernd and Braunschweig, Holger}, journal = {Journal of the American Chemical Society}, keywords = {ak-engel}, month = 10, number = 42, pages = {16954–16960}, publisher = {American Chemical Society (ACS)}, title = {Lewis-Base Stabilization of the Parent Al(I) Hydride under Ambient Conditions}, volume = 141, year = 2019 }
• A classical ride through a conical intersection. Schaupp, Thomas; Engel, Volker. In J. Chem. Phys., 150(3), S. 034301. American Institute of Physics, 2019.
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  @article{schaupp2019classical, abstract = {Regarding the correlated electron-nuclear motion in a model system, we investigate the dynamics in the vicinity of a conical intersection (CoIn) between two excited state potential surfaces. It is documented that an ensemble of classical trajectories which move in the complete electronic-nuclear phase space tracks the quantum wave-packet motion through the CoIn which is accompanied by a non-adiabatic population transfer. On the contrary, for an adiabatic circular motion around the position of the CoIn, the quantum mechanical and classical densities deviate substantially. In the latter case, the Born-Oppenheimer classical nuclear motion on a single potential surface is able to track the quantum dynamics.}, author = {Schaupp, Thomas and Engel, Volker}, booktitle = {The Journal of Chemical Physics}, journal = {J. Chem. Phys.}, keywords = {for1809}, month = {01}, number = 3, pages = {034301}, publisher = {American Institute of Physics}, title = {A classical ride through a conical intersection}, volume = 150, year = 2019 }
• On the calculation of time-dependent electron momenta within the Born-Oppenheimer approximation. Schaupp, Thomas; Engel, Volker. In J. Chem. Phys., 150(16), S. 164110. American Institute of Physics, 2019.
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  @article{noauthororeditor, author = {Schaupp, Thomas and Engel, Volker}, booktitle = {The Journal of Chemical Physics}, journal = {J. Chem. Phys.}, keywords = {ak-engel}, month = {04}, number = 16, pages = 164110, publisher = {American Institute of Physics}, title = {On the calculation of time-dependent electron momenta within the Born-Oppenheimer approximation}, volume = 150, year = 2019 }

• Time-dependent electron momenta from Born-Oppenheimer calculations. Schaupp, Thomas; Albert, Julian; Engel, Volker. In The European Physical Journal B, 91(6), S. 97. 2018.
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  @article{Schaupp2018, abstract = {The time-dependent expectation value of the electron momentum is zero if determined within the Born-Oppenheimer (BO) approximation. We show that one arrives at non-zero values, if the mean momentum is calculated from the time-derivative of the electronic coordinate. This is illustrated for the case of a coupled electron-nuclear motion in a one-dimensional model system. Regarding a situation where the BO approximation is valid, we find that the BO results are in perfect agreement with those derived from the numerically exact calculations. This holds for cases where the involved wave packets are well localized and also if a large spreading of the probability density occurs.}, author = {Schaupp, Thomas and Albert, Julian and Engel, Volker}, journal = {The European Physical Journal B}, keywords = {ak-engel}, month = {06}, number = 6, pages = 97, title = {Time-dependent electron momenta from Born-Oppenheimer calculations}, volume = 91, year = 2018 }
• Stochastically correlated versus uncorrelated quantum-state diffusion dynamics in different electronic states: third-order polarizations and two-dimensional vibronic spectra. Wehner, Johannes; Engel, Volker. In Chemical Physics, 515, S. 102–107. Elsevier {BV}, 2018.
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  @article{Wehner_2018, author = {Wehner, Johannes and Engel, Volker}, journal = {Chemical Physics}, keywords = {for1809}, month = 11, pages = {102-107}, publisher = {Elsevier {BV}}, title = {Stochastically correlated versus uncorrelated quantum-state diffusion dynamics in different electronic states: third-order polarizations and two-dimensional vibronic spectra}, volume = 515, year = 2018 }

• Correlated electron-nuclear dissociation dynamics: classical versus quantum motion. Schaupp, Thomas; Albert, Julian; Engel, Volker. In The European Physical Journal D, 71(4), S. 91. 2017.
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  @article{Schaupp2017, abstract = {We investigate the coupled electron-nuclear dynamics in a model system which undergoes dissociation. In choosing different initial conditions, the cases of adiabatic and non-adiabatic dissociation are realized. We treat the coupled electronic and nuclear motion in the complete configuration space so that classically, no surface hopping procedures have to be incorporated in the case that more than a single adiabatic electronic state is populated during the fragmentation. Due to the anharmonic interaction potential, it is expected that classical mechanics substantially deviate from quantum mechanics. However, we provide examples where the densities and fragmentation yields obtained from the two treatments are in astonishingly strong agreement in the case that one starts in the electronic ground state initially. As expected, larger deviations are found if one starts in electronically excited states where trajectories are sampled from the more spatially extended electronic wave function. In that case, higher initial energies are accessed, and the motion proceeds in regions with increasing degree of anharmonicity.}, author = {Schaupp, Thomas and Albert, Julian and Engel, Volker}, journal = {The European Physical Journal D}, keywords = {ak-engel}, number = 4, pages = 91, title = {Correlated electron-nuclear dissociation dynamics: classical versus quantum motion}, volume = 71, year = 2017 }
• On the time-dependent calculation of angular averaged vibronic absorption spectra with an application to molecular aggregates. Brüning, Christoph; Engel, Volker. In Chemical Physics, 482, S. 64–68. 2017.
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  @article{Brüning201764, abstract = {Abstract We introduce an efficient method to determine angular averaged absorption spectra for cases where electronic transitions take place to a manifold of N coupled excited states. The approach rests on the calculation of time-dependent auto-correlation functions which, upon Fourier-transform yield the spectrum. Assuming the Condon-approximation, it is shown that three wave-packet propagations are sufficient to calculate the spectrum. This is in contrast to a direct approach where it is necessary to perform N propagations to arrive at \{N2\} cross-correlation functions. The reduction in computation time is of importance for larger molecular aggregates where the number N is determined by the aggregate size. We provide an example by determining spectra for macrocyclic dyes in different dipole-geometries.}, author = {Brüning, Christoph and Engel, Volker}, journal = {Chemical Physics}, keywords = {ak-engel}, note = {Electrons and nuclei in motion - correlation and dynamics in molecules (on the occasion of the 70th birthday of Lorenz S. Cederbaum)}, pages = {64 - 68}, title = {On the time-dependent calculation of angular averaged vibronic absorption spectra with an application to molecular aggregates}, volume = 482, year = 2017 }
• Communication: On the calculation of time-dependent electron flux within the Born-Oppenheimer approximation: A flux-flux reflection principle. Albert, Julian; Hader, Kilian; Engel, Volker. In The Journal of Chemical Physics, 147(24), S. 241101. American Institute of Physics, 2017.
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  @article{albert2017communication, abstract = {It is commonly assumed that the time-dependent electron flux calculated within the Born-Oppenheimer (BO) approximation vanishes. This is not necessarily true if the flux is directly determined from the continuity equation obeyed by the electron density. This finding is illustrated for a one-dimensional model of coupled electronic-nuclear dynamics. There, the BO flux is in perfect agreement with the one calculated from a solution of the time-dependent Schrödinger equation for the coupled motion. A reflection principle is derived where the nuclear BO flux is mapped onto the electronic flux.}, author = {Albert, Julian and Hader, Kilian and Engel, Volker}, booktitle = {The Journal of Chemical Physics}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = 12, number = 24, pages = 241101, publisher = {American Institute of Physics}, title = {Communication: On the calculation of time-dependent electron flux within the Born-Oppenheimer approximation: A flux-flux reflection principle}, volume = 147, year = 2017 }
• Time-resolved photoelectron spectroscopy of IR-driven electron dynamics in a charge transfer model system. Falge, Mirjam; Frobel, Friedrich Georg; Engel, Volker; Gräfe, Stefanie. In Phys. Chem. Chem. Phys., 19(30), S. 19683–19690. The Royal Society of Chemistry, 2017.
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  @article{C7CP01832K, abstract = {If the adiabatic approximation is valid{,} electrons smoothly adapt to molecular geometry changes. In contrast{,} as a characteristic of diabatic dynamics{,} the electron density does not follow the nuclear motion. Recently{,} we have shown that the asymmetry in time-resolved photoelectron spectra serves as a tool to distinguish between these dynamics [Falge et al.{,} J. Phys. Chem. Lett.{,} 2012{,} 3{,} 2617]. Here{,} we investigate the influence of an additional{,} moderately intense infrared (IR) laser field{,} as often applied in attosecond time-resolved experiments{,} on such asymmetries. This is done using a simple model for coupled electronic-nuclear motion. We calculate time-resolved photoelectron spectra and their asymmetries and demonstrate that the spectra directly map the bound electron-nuclear dynamics. From the asymmetries{,} we can trace the IR field-induced population transfer and both the field-driven and intrinsic (non-)adiabatic dynamics. This holds true when considering superposition states accompanied by electronic coherences. The latter are observable in the asymmetries for sufficiently short XUV pulses to coherently probe the coupled states. It is thus documented that the asymmetry is a measure for phases in bound electron wave packets and non-adiabatic dynamics.}, author = {Falge, Mirjam and Frobel, Friedrich Georg and Engel, Volker and Gräfe, Stefanie}, journal = {Phys. Chem. Chem. Phys.}, keywords = {myown}, number = 30, pages = {19683-19690}, publisher = {The Royal Society of Chemistry}, title = {Time-resolved photoelectron spectroscopy of IR-driven electron dynamics in a charge transfer model system}, volume = 19, year = 2017 }
• Coupled electron-nuclear quantum dynamics through and around a conical intersection. Albert, Julian; Hader, Kilian; Engel, Volker. In The Journal of Chemical Physics, 147(6), S. 064302. {AIP} Publishing, 2017.
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  @article{Albert_2017, author = {Albert, Julian and Hader, Kilian and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {08}, number = 6, pages = {064302}, publisher = {{AIP} Publishing}, title = {Coupled electron-nuclear quantum dynamics through and around a conical intersection}, volume = 147, year = 2017 }
• The dimer-approach to characterize opto-electronic properties of and exciton trapping and diffusion in organic semiconductor aggregates and crystals. Engels, Bernd; Engel, Volker. In Phys. Chem. Chem. Phys., 19(20), S. 12604–12619. The Royal Society of Chemistry, 2017.
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  @article{C7CP01599B, abstract = {A fundamental understanding of photo-induced processes in opto-electronic thin film devices is a prerequisite for the rational design of improved organic semiconductor materials. Absorption and emission spectra provide important insights into the complicated electronic structure of and relaxation processes in organic semiconductor aggregates and crystals. They are of interest because they often limit the efficiencies of the devices. For an assignment of the spectra a close interplay between experiment and theory is essential because simulations are often necessary to entangle the various effects which determine the features of the spectra. In the present perspective we describe the so called dimer-approach and provide a few examples in which this approach could successfully deliver an atomistic picture of photo-induced relaxation effects in perylene-based materials and characterize their optical spectra. The model Hamiltonians of standard monomer-based approaches are also briefly discussed to reveal the differences between both methods and to shed some light on their strengths and shortcomings.}, author = {Engels, Bernd and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 20, pages = {12604-12619}, publisher = {The Royal Society of Chemistry}, title = {The dimer-approach to characterize opto-electronic properties of and exciton trapping and diffusion in organic semiconductor aggregates and crystals}, volume = 19, year = 2017 }
• Mapping of exciton-exciton annihilation in MEH-PPV by time-resolved spectroscopy: experiment and microscopic theory. Hader, Kilian; Consani, Cristina; Brixner, Tobias; Engel, Volker. In Phys. Chem. Chem. Phys., 19(47), S. 31989–31996. The Royal Society of Chemistry, 2017.
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  @article{C7CP05168A, abstract = {Transient absorption traces taken on samples of the polymer MEH-PPV are measured as a function of the laser intensity. In increasing the laser power{,} different decay dynamics of the signal are obtained. This suggests that effective exciton-exciton annihilation takes place. The signals are interpreted using a microscopic quantum mechanical model. The analysis points at an ultrafast excitonic decay via interchain and intrachain annihilation{,} where the latter process is roughly thirty times slower. Afterwards{,} diffusion-induced annihilation and relaxation become effective and thus determine the long-time behavior of the excited-state decay.}, author = {Hader, Kilian and Consani, Cristina and Brixner, Tobias and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 47, pages = {31989-31996}, publisher = {The Royal Society of Chemistry}, title = {Mapping of exciton-exciton annihilation in MEH-PPV by time-resolved spectroscopy: experiment and microscopic theory}, volume = 19, year = 2017 }
• Electron-nuclear wave-packet dynamics through a conical intersection. Hader, Kilian; Albert, Julian; Gross, E. K. U.; Engel, Volker. In The Journal of Chemical Physics, 146(7), S. 074304. {AIP} Publishing, 2017.
  • [ BibTeX ]
  • [ DOI ]
  @article{Hader_2017, author = {Hader, Kilian and Albert, Julian and Gross, E. K. U. and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {02}, number = 7, pages = {074304}, publisher = {{AIP} Publishing}, title = {Electron-nuclear wave-packet dynamics through a conical intersection}, volume = 146, year = 2017 }
• Geometrical Optimization Approach to Isomerization: Models and Limitations. Chang, Bo Y.; Shin, Seokmin; Engel, Volker; Sola, Ignacio R. In The Journal of Physical Chemistry A, 121(43), S. 8280–8287. 2017.
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  @article{doi:10.1021/acs.jpca.7b08767, abstract = {We study laser-driven isomerization reactions through an excited electronic state using the recently developed Geometrical Optimization procedure. Our goal is to analyze whether an initial wave packet in the ground state, with optimized amplitudes and phases, can be used to enhance the yield of the reaction at faster rates, driven by a single picosecond pulse or a pair of femtosecond pulses resonant with the electronic transition. We show that the symmetry of the system imposes limitations in the optimization procedure, such that the method rediscovers the pump-dump mechanism.}, author = {Chang, Bo Y. and Shin, Seokmin and Engel, Volker and Sola, Ignacio R.}, journal = {The Journal of Physical Chemistry A}, keywords = {myown}, note = {PMID: 28994591}, number = 43, pages = {8280-8287}, title = {Geometrical Optimization Approach to Isomerization: Models and Limitations}, volume = 121, year = 2017 }
• The electronic character of PTCDA thin films in comparison to other perylene-based organic semi-conductors: ab initio-{,} TD-DFT and semi-empirical computations of the opto-electronic properties of large aggregates. Bellinger, Daniel; Pflaum, Jens; Brüning, Christoph; Engel, Volker; Engels, Bernd. In Phys. Chem. Chem. Phys., 19(3), S. 2434–2448. The Royal Society of Chemistry, 2017.
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  @article{C6CP07673D, abstract = {Perylene-based compounds are promising materials for opto-electronic thin film devices but despite intense investigations{,} important details of their electronic structure are still under debate. For perylene-3{,}4{,}9{,}10-tetracarboxylic dianhydrid (PTCDA){,} the theoretical models predict a different relative energetic order of Frenkel and Charge Transfer (CT) states. Additionally{,} while one model indicates strong differences between PTCDA on one hand and other perylene-based compounds on the other{,} recent ab initio computations indicate electronic properties of all perylene-based compounds to resemble each other. Finally{,} the models disagree about the amount of mixing between CT and Frenkel states. Definitive answers to these questions are difficult because the approaches use various approximations. Up to date{,} the ab initio based methods employ rather small model systems and neglect environmental effects. In the present work{,} we improve our former approach by analyzing the effects of the various simplifications. In more detail{,} we increase the size of the model systems{,} include environmental effects and investigate the influence of exciton-phonon couplings on the absorption spectrum. The computations for larger aggregates were performed with the ZINDO/S approach{,} because benchmark computations show that it provides accurate vertical excitation energies for Frenkel{,} as well as CT states.}, author = {Bellinger, Daniel and Pflaum, Jens and Brüning, Christoph and Engel, Volker and Engels, Bernd}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 3, pages = {2434-2448}, publisher = {The Royal Society of Chemistry}, title = {The electronic character of PTCDA thin films in comparison to other perylene-based organic semi-conductors: ab initio-{,} TD-DFT and semi-empirical computations of the opto-electronic properties of large aggregates}, volume = 19, year = 2017 }

• Two-dimensional femtosecond optical spectroscopy of trapping dynamics in a charge-transfer process. Keß, Martin; Engel, Volker. In Chemical Physics Letters, 650, S. 41–46. 2016.
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  @article{KE201641, author = {Keß, Martin and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, pages = {41 - 46}, title = {Two-dimensional femtosecond optical spectroscopy of trapping dynamics in a charge-transfer process}, volume = 650, year = 2016 }
• Two-dimensional vibronic spectroscopy of molecular aggregates: Trimers, dimers, and monomers. Keß, M.; Worth, G.; Engel, V. In The Journal of Chemical Physics, 145(8), S. 084305. {AIP} Publishing, 2016.
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  @article{Ke__2016, author = {Ke{\ss}, M. and Worth, G. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {08}, number = 8, pages = {084305}, publisher = {{AIP} Publishing}, title = {Two-dimensional vibronic spectroscopy of molecular aggregates: Trimers, dimers, and monomers}, volume = 145, year = 2016 }
• Identification of effective exciton-exciton annihilation in squaraine-squaraine copolymers. Hader, Kilian; May, Volkhard; Lambert, Christoph; Engel, Volker. In Phys. Chem. Chem. Phys., 18(19), S. 13368–13374. The Royal Society of Chemistry, 2016.
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  @article{C6CP01780K, abstract = {Ultrafast time-resolved transient absorption spectroscopy is able to monitor the fate of the excited state population in molecular aggregates or polymers. Due to many competing decay processes{,} the identification of exciton-exciton annihilation (EEA) is difficult. Here{,} we use a microscopic model to describe exciton annihilation processes in squaraine-squaraine copolymers. Transient absorption time traces measured at different laser powers exhibit an unusual time-dependence. The analysis points towards dynamics taking place on three time-scales. Immediately after laser-excitation a localization of excitons takes place within the femtosecond time-regime. This is followed by exciton-exciton annihilation which is responsible for a fast decay of the exciton population. At later times{,} excitations being localized on units which are not directly connected remain so that diffusion dominates the dynamics and leads to a slower decay. We thus provide evidence for EEA tracked by time-resolved spectroscopy which has not been reported that clearly before.}, author = {Hader, Kilian and May, Volkhard and Lambert, Christoph and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 19, pages = {13368-13374}, publisher = {The Royal Society of Chemistry}, title = {Identification of effective exciton-exciton annihilation in squaraine-squaraine copolymers}, volume = 18, year = 2016 }
• Two-dimensional optical spectroscopy of homo- and heterodimers. Wehner, Johannes; Engel, Volker. In Phys. Chem. Chem. Phys., 18(48), S. 32910–32920. The Royal Society of Chemistry, 2016.
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  @article{C6CP04936B, abstract = {We theoretically study the two-dimensional (2D) spectroscopy of molecular dimers. The spectra are first analyzed within an electronic level model. It is demonstrated how the angular average over molecular orientations influences the features of the spectra. Methods to calculate angular averaged vibronic spectra within perturbation theory are compared. We systematically document changes in the 2D-spectra upon going from homo- to heterodimers. In particular{,} it is demonstrated that large-amplitude off-diagonal peaks appear for heterodimers even in the limit of vanishing coupling. This is related to the difference in the excitation energies of the two different monomers. For homodimers with equal monomer excitation energies{,} such peaks become diagonal peaks and thus cannot be isolated.}, author = {Wehner, Johannes and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 48, pages = {32910-32920}, publisher = {The Royal Society of Chemistry}, title = {Two-dimensional optical spectroscopy of homo- and heterodimers}, volume = 18, year = 2016 }
• Femtosecond time-resolved four-wave mixing spectroscopy of coupled electron-nuclear motion. Albert, Julian; Engel, Volker. In Asian Journal of Physics, 25(2), S. 189–197. 2016.
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  @article{noauthororeditor, abstract = {We present a theoretical study of time-resolved four-wave mixing (FWM) spectroscopy on a model system describing coupled electron-nuclear dynamics. Changing the parameterization of the Coulomb-interaction, two situations can be created. In one case, the Born-Oppenheimer adiabatic approximation holds. In adjusting the pulse sequence it is then possible to separately monitor ground state and excited state vibrational wave-packet dynamics. In the second case, strong non-adiabatic coupling is present so that the separation of ground- and excited state nuclear dynamics becomes difficult. To investigate details of the dynamics and its relation to the spectroscopy, we compare FWM-signals obtained from an exact numerical calculation to those obtained within the adiabatic approximation.}, author = {Albert, Julian and Engel, Volker}, journal = {Asian Journal of Physics}, keywords = {for1809}, note = {Dedicated to Professor Wolfgang Kiefer on the occasion of his 75th birthday}, number = 2, pages = {189-197}, title = {Femtosecond time-resolved four-wave mixing spectroscopy of coupled electron-nuclear motion}, volume = 25, year = 2016 }
• How fast is optically induced electron transfer in organic mixed valence systems?. Lambert, C.; Moos, M.; Schmiedel, A.; Holzapfel, M.; Schafer, J.; Kess, M.; Engel, V. In Phys. Chem. Chem. Phys., 18(28), S. 19405–19411. The Royal Society of Chemistry, 2016.
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  @article{C6CP03053J, abstract = {The rate of thermally induced electron transfer in organic mixed valence compounds has thoroughly been investigated by e.g. temperature dependent ESR spectroscopy. However{,} almost nothing is known about the dynamics of optically induced electron transfer processes in such systems. Therefore{,} we investigated these processes in mixed valence compounds based on triphenylamine redox centres bridged by conjugated spacers by NIR transient absorption spectroscopy with fs-time resolution. These experiments revealed an internal conversion (IC) process to be on the order of 50-200 fs which is equivalent to the back electron transfer after optical excitation into the intervalence charge transfer band. This IC is followed by ultrafast cooling to the ground state within 1 ps. Thus{,} in the systems investigated optically induced electron transfer is about 3-4 orders of magnitude faster than thermally induced ET.}, author = {Lambert, C. and Moos, M. and Schmiedel, A. and Holzapfel, M. and Schafer, J. and Kess, M. and Engel, V.}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 28, pages = {19405-19411}, publisher = {The Royal Society of Chemistry}, title = {How fast is optically induced electron transfer in organic mixed valence systems?}, volume = 18, year = 2016 }
• Exciton dynamics in perturbed vibronic molecular aggregates. Brüning, C.; Wehner, J.; Hausner, J.; Wenzel, M.; Engel, V. In Structural Dynamics, 3(4), S. 043201. {AIP} Publishing, 2016.
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  @article{Br_ning_2016, author = {Brüning, C. and Wehner, J. and Hausner, J. and Wenzel, M. and Engel, V.}, journal = {Structural Dynamics}, keywords = {ak-engel}, month = {07}, number = 4, pages = {043201}, publisher = {{AIP} Publishing}, title = {Exciton dynamics in perturbed vibronic molecular aggregates}, volume = 3, year = 2016 }
• Exciton-Vibrational Couplings in Homo- and Heterodimer Stacks of Perylene Bisimide Dyes within Cyclophanes: Studies on Absorption Properties and Theoretical Analysis. Bialas, David; Brüning, Christoph; Schlosser, Felix; Fimmel, Benjamin; Thein, Johannes; Engel, Volker; Würthner, Frank. In Chemistry – A European Journal, 22(42), S. 15011–15018. 2016.
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  @article{CHEM:CHEM201603205, abstract = {The optical properties of a series of three cyclophanes comprising either identical or different perylene bisimide (PBI) chromophores were studied by UV/Vis absorption spectroscopy and their distinctive spectral features were analyzed. All the investigated cyclophanes show significantly different absorption features with respect to the corresponding constituent PBI monomers indicating strong coupling interactions between the PBI units within the cyclophanes. DFT calculations suggest a π-stacked arrangement of the PBI units at close van der Waals distance in the cyclophanes with rotational displacement. Simulations of the absorption spectra based on time-dependent quantum mechanics properly reproduced the experimental spectra, revealing exciton-vibrational coupling between the chromophores both in homo- and heterodimer stacks. The PBI cyclophane comprising two different PBI chromophores represents the first example of a PBI heterodimer stack for which the exciton coupling has been investigated. The quantum dynamics analysis reveals that exciton coupling in heteroaggregates is indeed of similar strength as for homoaggregates.}, author = {Bialas, David and Brüning, Christoph and Schlosser, Felix and Fimmel, Benjamin and Thein, Johannes and Engel, Volker and Würthner, Frank}, journal = {Chemistry – A European Journal}, keywords = {ak-engel}, number = 42, pages = {15011–15018}, title = {Exciton-Vibrational Couplings in Homo- and Heterodimer Stacks of Perylene Bisimide Dyes within Cyclophanes: Studies on Absorption Properties and Theoretical Analysis}, volume = 22, year = 2016 }
• Communication: Adiabatic and non-adiabatic electron-nuclear motion: Quantum and classical dynamics. Albert, Julian; Kaiser, Dustin; Engel, Volker. In The Journal of Chemical Physics, 144(17), S. 171103. {AIP} Publishing, 2016.
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  • [ DOI ]
  @article{Albert_2016, author = {Albert, Julian and Kaiser, Dustin and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {05}, number = 17, pages = 171103, publisher = {{AIP} Publishing}, title = {Communication: Adiabatic and non-adiabatic electron-nuclear motion: Quantum and classical dynamics}, volume = 144, year = 2016 }

• Communication: Vibrational and vibronic coherences in the two dimensional spectroscopy of coupled electron-nuclear motion. Albert, Julian; Falge, Mirjam; Gomez, Sandra; Sola, Ignacio R.; Hildenbrand, Heiko; Engel, Volker. In The Journal of Chemical Physics, 143(4), S. 041102. {AIP} Publishing, 2015.
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  @article{Albert_2015, author = {Albert, Julian and Falge, Mirjam and Gomez, Sandra and Sola, Ignacio R. and Hildenbrand, Heiko and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {07}, number = 4, pages = {041102}, publisher = {{AIP} Publishing}, title = {Communication: Vibrational and vibronic coherences in the two dimensional spectroscopy of coupled electron-nuclear motion}, volume = 143, year = 2015 }
• Macrocyclic cis-Indolenine Squaraine Dyes as Efficient Near Infrared Emitters. Brüning, Christoph; Welz, Eileen; Heilos, Anna; Stehr, Vera; Walter, Christof; Engels, Bernd; Völker, Sebastian F.; Lambert, Christoph; Engel, Volker. In The Journal of Physical Chemistry C, 119(11), S. 6174–6180. 2015.
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  @article{doi:10.1021/jp5120916, abstract = {The absorption and emission properties of macrocyclic cis-indolenine squaraine dyes are studied experimentally and theoretically. As compared to the monomeric species, large Stokes shifts of the emission are observed for cyclic trimers and tetramers. The theoretical analysis predicts that these shifts are caused by deviations of the excited state geometries from the strictly symmetric configurations. Breaking the symmetry makes fluorescence from lower excited states possible which otherwise is forbidden. The line shapes of the spectra are dominated by vibronic structures which can be identified using a vibronic coupling model. From the results, the important fact emerges that macrocyclic squaraine aggregates can be effectively used as building blocks for near-infrared (NIR) emitters.}, author = {Brüning, Christoph and Welz, Eileen and Heilos, Anna and Stehr, Vera and Walter, Christof and Engels, Bernd and Völker, Sebastian F. and Lambert, Christoph and Engel, Volker}, journal = {The Journal of Physical Chemistry C}, keywords = {ak-engel}, number = 11, pages = {6174-6180}, title = {Macrocyclic cis-Indolenine Squaraine Dyes as Efficient Near Infrared Emitters}, volume = 119, year = 2015 }
• Extended quantum jump description of vibronic two-dimensional spectroscopy. Albert, Julian; Falge, Mirjam; Keß, Martin; Wehner, Johannes G.; Zhang, Pan-Pan; Eisfeld, Alexander; Engel, Volker. In The Journal of Chemical Physics, 142(21), S. 212440. {AIP} Publishing, 2015.
  • [ BibTeX ]
  • [ DOI ]
  @article{Albert_2015, author = {Albert, Julian and Falge, Mirjam and Ke{\ss}, Martin and Wehner, Johannes G. and Zhang, Pan-Pan and Eisfeld, Alexander and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {06}, number = 21, pages = 212440, publisher = {{AIP} Publishing}, title = {Extended quantum jump description of vibronic two-dimensional spectroscopy}, volume = 142, year = 2015 }

• Multiple time scale population transfer-dynamics in coupled electronic states. Kess, Martin; Brüning, Christoph; Engel, Volker. In Chemical Physics, 442, S. 26–30. 2014.
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  @article{KESS201426, author = {Kess, Martin and Brüning, Christoph and Engel, Volker}, journal = {Chemical Physics}, keywords = {ak-engel}, note = {Papers from the 11th International Conference on Femtochemistry (FEMTO11) that took place at The Technical University of Denmark (DTU), Copenhagen}, pages = {26 - 30}, title = {Multiple time scale population transfer-dynamics in coupled electronic states}, volume = 442, year = 2014 }
• Identification of Ultrafast Relaxation Processes As a Major Reason for Inefficient Exciton Diffusion in Perylene-Based Organic Semiconductors. Settels, Volker; Schubert, Alexander; Tafipolski, Maxim; Liu, Wenlan; Stehr, Vera; Topczak, Anna K.; Pflaum, Jens; Deibel, Carsten; Fink, Reinhold F.; Engel, Volker; Engels, Bernd. In Journal of the American Chemical Society, 136(26), S. 9327–9337. 2014.
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  @article{doi:10.1021/ja413115h, abstract = {The exciton diffusion length (LD) is a key parameter for the efficiency of organic optoelectronic devices. Its limitation to the nm length scale causes the need of complex bulk-heterojunction solar cells incorporating difficulties in long-term stability and reproducibility. A comprehensive model providing an atomistic understanding of processes that limit exciton trasport is therefore highly desirable and will be proposed here for perylene-based materials. Our model is based on simulations with a hybrid approach which combines high-level ab initio computations for the part of the system directly involved in the described processes with a force field to include environmental effects. The adequacy of the model is shown by detailed comparison with available experimental results. The model indicates that the short exciton diffusion lengths of α-perylene tetracarboxylicdianhydride (PTCDA) are due to ultrafast relaxation processes of the optical excitation via intermolecular motions leading to a state from which further exciton diffusion is hampered. As the efficiency of this mechanism depends strongly on molecular arrangement and environment, the model explains the strong dependence of LD on the morphology of the materials, for example, the differences between α-PTCDA and diindenoperylene. Our findings indicate how relaxation processes can be diminished in perylene-based materials. This model can be generalized to other organic compounds.}, author = {Settels, Volker and Schubert, Alexander and Tafipolski, Maxim and Liu, Wenlan and Stehr, Vera and Topczak, Anna K. and Pflaum, Jens and Deibel, Carsten and Fink, Reinhold F. and Engel, Volker and Engels, Bernd}, journal = {Journal of the American Chemical Society}, keywords = {ak-engel}, note = {PMID: 24909402}, number = 26, pages = {9327-9337}, title = {Identification of Ultrafast Relaxation Processes As a Major Reason for Inefficient Exciton Diffusion in Perylene-Based Organic Semiconductors}, volume = 136, year = 2014 }
• Coherent and incoherent contributions to the carrier-envelope phase control of wave packet localization in quantum double wells. Hader, K.; Engel, V. In The Journal of Chemical Physics, 140(18), S. 184316. {AIP} Publishing, 2014.
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  @article{Hader_2014, author = {Hader, K. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {05}, number = 18, pages = 184316, publisher = {{AIP} Publishing}, title = {Coherent and incoherent contributions to the carrier-envelope phase control of wave packet localization in quantum double wells}, volume = 140, year = 2014 }
• Quantum diffusion wave-function approach to two-dimensional vibronic spectroscopy. Wehner, Johannes; Falge, Mirjam; Strunz, Walter T.; Engel, Volker. In The Journal of Chemical Physics, 141(13), S. 134306. {AIP} Publishing, 2014.
  • [ BibTeX ]
  • [ DOI ]
  @article{Wehner_2014, author = {Wehner, Johannes and Falge, Mirjam and Strunz, Walter T. and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = 10, number = 13, pages = 134306, publisher = {{AIP} Publishing}, title = {Quantum diffusion wave-function approach to two-dimensional vibronic spectroscopy}, volume = 141, year = 2014 }
• The time-scale of nonlinear events driven by strong fields: can one control the spin coupling before ionization runs over?. Falge, Mirjam; Vindel-Zandbergen, Patricia; Engel, Volker; Lein, Manfred; Chang, Bo Y; Sola, Ignacio R. In Journal of Physics B: Atomic, Molecular and Optical Physics, 47(12), S. 124027. 2014.
  • [ BibTeX ]
  @article{0953-4075-47-12-124027, abstract = {An initially populated spin state of an ion chain interacting with an external field can decay via spin coupling or via ionization. Using a simple two-level Hamiltonian we investigate the relation between spin-coupling and ionization rate and identify conditions for an efficient spin-control via a non-resonant Stark effect by suppressing ionization. The results are confirmed in solving the time-dependent Schrödinger equation for the interaction of a laser field with a spin-coupled model system where two electrons and a nucleus move in a collinear configuration. It is thus shown, that quantum control of intersystem crossing can indeed be effective if the intensity of the external field and the accompanying Stark-shift is adjusted properly to the spin-coupling strength.}, author = {Falge, Mirjam and Vindel-Zandbergen, Patricia and Engel, Volker and Lein, Manfred and Chang, Bo Y and Sola, Ignacio R}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, keywords = {ak-engel}, number = 12, pages = 124027, title = {The time-scale of nonlinear events driven by strong fields: can one control the spin coupling before ionization runs over?}, volume = 47, year = 2014 }
• Theoretical Analysis of the Relaxation Dynamics in Perylene Bisimide Dimers Excited by Femtosecond Laser Pulses. Schubert, Alexander; Falge, Mirjam; Kess, Martin; Settels, Volker; Lochbrunner, Stefan; Strunz, Walter T.; Würthner, Frank; Engels, Bernd; Engel, Volker. In The Journal of Physical Chemistry A, 118(8), S. 1403–1412. 2014.
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  @article{doi:10.1021/jp412166a, abstract = {We present a model for the relaxation dynamics in perylene bisimide dimers, which is based on ab initio electronic structure and quantum dynamics calculations including effects of dissipation. The excited-state dynamics proceeds via a mixing of electronic states of local Frenkel and charge-transfer characters, which becomes effective upon a small distortion of the dimer geometry. In this way, it is possible to explain the fast depopulation of the photoexcited state, which we characterize by femtosecond transient absorption measurements. The combined theoretical and experimental analysis hints at a trapping mechanism, which involves nonadiabatic and dissipative dynamics in an excited-state vibronic manifold and provides an atomistic picture that might prove valuable for future design of photovoltaic materials.}, author = {Schubert, Alexander and Falge, Mirjam and Kess, Martin and Settels, Volker and Lochbrunner, Stefan and Strunz, Walter T. and Würthner, Frank and Engels, Bernd and Engel, Volker}, journal = {The Journal of Physical Chemistry A}, keywords = {ak-engel}, note = {PMID: 24475775}, number = 8, pages = {1403-1412}, title = {Theoretical Analysis of the Relaxation Dynamics in Perylene Bisimide Dimers Excited by Femtosecond Laser Pulses}, volume = 118, year = 2014 }
• Singlet–Singlet Exciton Annihilation in an Exciton-Coupled Squaraine-Squaraine Copolymer: A Model toward Hetero-J-Aggregates. Völker, Sebastian F.; Schmiedel, Alexander; Holzapfel, Marco; Renziehausen, Klaus; Engel, Volker; Lambert, Christoph. In The Journal of Physical Chemistry C, 118(31), S. 17467–17482. 2014.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jp5055809, abstract = {Low-band-gap polymers with broad spectral absorption are highly sought after for application in organic photovoltaic cells and other optoelectronic devices. Thus, a conjugated copolymer based on two different indolenine squaraine dyes SQA and SQB was synthesized by Suzuki coupling, and its steady-state and time-resolved optical properties were investigated in detail. In CHCl3 the copolymer [SQA-SQB]n shows a strongly broadened and red-shifted absorption compared to that of its monomers, which was explained by exciton coupling of localized transition moments. The theoretical background of exciton coupling theory for copolymers was worked out in detail. In toluene, [SQA-SQB]n displays a spectral narrowing of the lowest excitation band which resembles the exchange narrowing effect found in cyanine J-aggregates. In this way [SQA-SQB]n behaves like a one-dimensional covalently bound hetero-J-aggregate. The photoinduced dynamics of the copolymer was investigated by transient absorption pump–probe spectroscopy with femtosecond resolution. Because of the unusually high exciton diffusion constant, singlet–singlet annihilation is the rate-limiting step for deactivation of the copolymer in solution at high laser fluencies. This is unlike the situation for many conjugated polymers in the solid state, where diffusion-limited annihilation is usually found. Thus, the [SQA-SQB]n copolymer is a unique model system which combines the excitonic features of J-aggregates with the chemical robustness of a polymer.}, author = {Völker, Sebastian F. and Schmiedel, Alexander and Holzapfel, Marco and Renziehausen, Klaus and Engel, Volker and Lambert, Christoph}, journal = {The Journal of Physical Chemistry C}, keywords = {ak-engel}, number = 31, pages = {17467-17482}, title = {Singlet–Singlet Exciton Annihilation in an Exciton-Coupled Squaraine-Squaraine Copolymer: A Model toward Hetero-J-Aggregates}, volume = 118, year = 2014 }

• Carrier envelope phase effects induced by weak multicycle pulses: Localized quantum dynamics in double well potentials. Hader, Kilian; Renziehausen, Klaus; Engel, Volker. In Chemical Physics Letters, 579, S. 23–27. 2013.
  • [ BibTeX ]
  • [ DOI ]
  @article{HADER201323, author = {Hader, Kilian and Renziehausen, Klaus and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, pages = {23 - 27}, title = {Carrier envelope phase effects induced by weak multicycle pulses: Localized quantum dynamics in double well potentials}, volume = 579, year = 2013 }
• Manipulating the singlet--triplet transition in ion strings by nonresonant dynamic Stark effect. Vindel-Zandbergen, Patricia; Falge, Mirjam; Chang, Bo Y.; Engel, Volker; Sola, Ignacio R. In Theoretical Chemistry Accounts, 132(6), S. 1359. 2013.
  • [ BibTeX ]
  • [ DOI ]
  @article{Vindel-Zandbergen2013, abstract = {Using strong laser pulses, we show that it is possible to control the spin state in a model system based on a two-electron extension with spin couplings of the Shin–Metiu Hamiltonian, truncated to account for the lowest electronic energy states. We consider two different models depending on the number of electronic states included in the calculation. The initial electronic state determines when the spin state is stable or not in the absence of an external field. In the latter case, by nonresonant dynamic Stark effect, we show that it is possible to avoid spin transitions with strong fields, using different pulse frequencies. This effective spin locking requires minimizing absorption to excited singlets as well as decoupling the singlet and triplet electronic states. In the first case, we show that it is possible to force the spin transition by a combination of two pulses, a chirped pulse and a transform limited pulse, where the time-delay must be chosen to maximize spin switching on a different electronic state. Our results show that forcing the spin switching is a more difficult goal than avoiding it and that this goal becomes highly restricted when many electronic pathways or multi-photon processes are available.}, author = {Vindel-Zandbergen, Patricia and Falge, Mirjam and Chang, Bo Y. and Engel, Volker and Sola, Ignacio R.}, journal = {Theoretical Chemistry Accounts}, keywords = {ak-engel}, number = 6, pages = 1359, title = {Manipulating the singlet–triplet transition in ion strings by nonresonant dynamic Stark effect}, volume = 132, year = 2013 }
• Two-dimensional vibronic spectroscopy of molecular predissociation. Albert, Julian; Schubert, Alexander; Engel, Volker. In New Journal of Physics, 15(2), S. 025008. 2013.
  • [ BibTeX ]
  • [ DOI ]
  @article{1367-2630-15-2-025008, abstract = {We calculate two-dimensional (2D) spectra reflecting the time-dependent electronic predissociation of a diatomic molecule. The laser-excited electronic state is coupled non-adiabatically to a fragment channel, leading to the decay of the prepared quasi-bound states. This decay can be monitored by the three-pulse configuration employed in optical 2D spectroscopy. It is shown that in this way it is possible to state-selectively characterize the time-dependent population of resonance states with different lifetimes. A model of the NaI molecule serves as a numerical example.}, author = {Albert, Julian and Schubert, Alexander and Engel, Volker}, journal = {New Journal of Physics}, keywords = {ak-engel}, number = 2, pages = {025008}, title = {Two-dimensional vibronic spectroscopy of molecular predissociation}, volume = 15, year = 2013 }
• Weak-Field, Multiple-Cycle Carrier Envelope Phase Effects in Laser Excitation. Renziehausen, Klaus; Hader, Kilian; Jakubetz, Werner; Engel, Volker. In ChemPhysChem, 14(7), S. 1464–1470. WILEY-VCH Verlag, 2013.
  • [ BibTeX ]
  • [ DOI ]
  @article{CPHC:CPHC201200946, abstract = {Although the absolute or carrier envelope phase (CEP) of a laser pulse is usually assumed to be effective for ultrashort and/or ultrastrong pulses only, it is demonstrated that these limitations can eventually be removed. Therefore, the excitation of a model positively charged homonuclear diatomic molecule, in which four electronic states are coupled by the laser field, is studied. In an initial step, nuclear wave packets in two dissociative states are prepared. Upon reaching the fragment channel, a weak pulse interacts with the system and prepares CEP-dependent asymmetries associated with electron density localized on one or the other fragmentation product.}, author = {Renziehausen, Klaus and Hader, Kilian and Jakubetz, Werner and Engel, Volker}, journal = {ChemPhysChem}, keywords = {ak-engel}, number = 7, pages = {1464–1470}, publisher = {WILEY-VCH Verlag}, title = {Weak-Field, Multiple-Cycle Carrier Envelope Phase Effects in Laser Excitation}, volume = 14, year = 2013 }
• H₂CN⁺ and H₂CNH⁺: New insight into the structure and dynamics from mass-selected threshold photoelectron spectra. Holzmeier, Fabian; Lang, Melanie; Hader, Kilian; Hemberger, Patrick; Fischer, Ingo. In The Journal of Chemical Physics, 138(21), S. 214310. {AIP} Publishing, 2013.
  • [ BibTeX ]
  • [ DOI ]
  @article{Holzmeier_2013, author = {Holzmeier, Fabian and Lang, Melanie and Hader, Kilian and Hemberger, Patrick and Fischer, Ingo}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {06}, number = 21, pages = 214310, publisher = {{AIP} Publishing}, title = {H₂CN⁺ and H₂CNH⁺: New insight into the structure and dynamics from mass-selected threshold photoelectron spectra}, volume = 138, year = 2013 }
• Ultrafast Exciton Self-Trapping upon Geometry Deformation in Perylene-Based Molecular Aggregates. Schubert, Alexander; Settels, Volker; Liu, Wenlan; Würthner, Frank; Meier, Christoph; Fink, Reinhold F.; Schindlbeck, Stefan; Lochbrunner, Stefan; Engels, Bernd; Engel, Volker. In The Journal of Physical Chemistry Letters, 4(5), S. 792–796. 2013.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jz4000752, abstract = {Femtosecond time-resolved experiments demonstrate that the photoexcited state of perylene tetracarboxylic acid bisimide (PBI) aggregates in solution decays nonradiatively on a time-scale of 215 fs. High-level electronic structure calculations on dimers point toward the importance of an excited state intermolecular geometry distortion along a reaction coordinate that induces energy shifts and couplings between various electronic states. Time-dependent wave packet calculations incorporating a simple dissipation mechanism indicate that the fast energy quenching results from a doorway state with a charge-transfer character that is only transiently populated. The identified relaxation mechanism corresponds to a possible exciton trap in molecular materials.}, author = {Schubert, Alexander and Settels, Volker and Liu, Wenlan and Würthner, Frank and Meier, Christoph and Fink, Reinhold F. and Schindlbeck, Stefan and Lochbrunner, Stefan and Engels, Bernd and Engel, Volker}, journal = {The Journal of Physical Chemistry Letters}, keywords = {ak-engel}, note = {PMID: 26281934}, number = 5, pages = {792-796}, title = {Ultrafast Exciton Self-Trapping upon Geometry Deformation in Perylene-Based Molecular Aggregates}, volume = 4, year = 2013 }
• On the parameterization of vibronic Hamiltonians for molecular aggregates using absorption line-shapes as an input. Brüning, C.; Renziehausen, K.; Engel, V. In The Journal of Chemical Physics, 139(5), S. 054303. {AIP} Publishing, 2013.
  • [ BibTeX ]
  • [ DOI ]
  @article{Br_ning_2013, author = {Brüning, C. and Renziehausen, K. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {08}, number = 5, pages = {054303}, publisher = {{AIP} Publishing}, title = {On the parameterization of vibronic Hamiltonians for molecular aggregates using absorption line-shapes as an input}, volume = 139, year = 2013 }

• Fingerprints of Adiabatic versus Diabatic Vibronic Dynamics in the Asymmetry of Photoelectron Momentum Distributions. Falge, Mirjam; Engel, Volker; Gräfe, Stefanie. In The Journal of Physical Chemistry Letters, 3(18), S. 2617–2620. 2012.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jz3009826, abstract = {When the Born–Oppenheimer approximation is valid, electrons adiabatically follow the nuclear motion in molecules. For strong nonadiabatic coupling between electronic states, one encounters a diabatic motion where the electrons remain local and do not adapt to molecular geometry changes. We show that the mentioned limiting cases are reflected differently in the asymmetry of time-resolved photoelectron momentum distributions. Whereas for adiabatic dynamics, the asymmetry directly maps the time-dependent average nuclear momentum, in the diabatic case, the asymmetry is determined by a nonclassical interference effect arising from the mixing of wave function components in different electronic states, which is present at times nonadiabatic transitions take place.}, author = {Falge, Mirjam and Engel, Volker and Gräfe, Stefanie}, journal = {The Journal of Physical Chemistry Letters}, keywords = {ak-engel}, note = {PMID: 23378888}, number = 18, pages = {2617-2620}, title = {Fingerprints of Adiabatic versus Diabatic Vibronic Dynamics in the Asymmetry of Photoelectron Momentum Distributions}, volume = 3, year = 2012 }
• Vibronic energy localization in weakly coupled small molecular aggregates. Wehner, Johannes; Schubert, Alexander; Engel, Volker. In Chemical Physics Letters, 541, S. 49–53. 2012.
  • [ BibTeX ]
  • [ DOI ]
  @article{WEHNER201249, author = {Wehner, Johannes and Schubert, Alexander and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, pages = {49 - 53}, title = {Vibronic energy localization in weakly coupled small molecular aggregates}, volume = 541, year = 2012 }
• On the Divergence of Time-Dependent Perturbation Theory Applied to Laser-Induced Molecular Transitions: Analytical Calculations for the Simple Algorithm. Renziehausen, Klaus. In Journal of Physical Mathematics, 4, S. 1–12. {OMICS} Publishing Group, 2012.
  • [ BibTeX ]
  • [ DOI ]
  @article{Renziehausen2012, author = {Renziehausen, Klaus}, journal = {Journal of Physical Mathematics}, keywords = {ak-engel}, pages = {1–12}, publisher = {{OMICS} Publishing Group}, title = {On the Divergence of Time-Dependent Perturbation Theory Applied to Laser-Induced Molecular Transitions: Analytical Calculations for the Simple Algorithm}, volume = 4, year = 2012 }
• Adiabaticity in the lateral electron-momentum distribution after strong-field ionization. Henkel, Jost; Lein, Manfred; Engel, Volker; Dreissigacker, Ingo. In Phys. Rev. A, 85(2), S. 021402. American Physical Society, 2012.
  • [ BibTeX ]
  • [ DOI ]
  @article{PhysRevA.85.021402, author = {Henkel, Jost and Lein, Manfred and Engel, Volker and Dreissigacker, Ingo}, journal = {Phys. Rev. A}, keywords = {ak-engel}, month = {02}, number = 2, pages = {021402}, publisher = {American Physical Society}, title = {Adiabaticity in the lateral electron-momentum distribution after strong-field ionization}, volume = 85, year = 2012 }
• Fragment momentum distributions obtained from coupled electron-nuclear dynamics. Hader, Kilian; Engel, Volker. In The Journal of Chemical Physics, 136(10), S. 104306. {AIP} Publishing, 2012.
  • [ BibTeX ]
  • [ DOI ]
  @article{Hader_2012, author = {Hader, Kilian and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {03}, number = 10, pages = 104306, publisher = {{AIP} Publishing}, title = {Fragment momentum distributions obtained from coupled electron-nuclear dynamics}, volume = 136, year = 2012 }
• Quantum Wave-Packet Dynamics in Spin-Coupled Vibronic States. Falge, Mirjam; Engel, Volker; Lein, Manfred; Vindel-Zandbergen, Patricia; Chang, Bo Y.; Sola, Ignacio R. In The Journal of Physical Chemistry A, 116(46), S. 11427–11433. 2012.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jp306566x, abstract = {Extending the Shin–Metiu two-electron Hamiltonian, we construct a new Hamiltonian with effective singlet–triplet couplings. The Born–Oppenheimer electronic potentials and couplings are obtained for different parameters, and the laser-free dynamics is calculated with the full Hamiltonian and in the adiabatic limit. We compare the dynamics of the system using nuclear wave packets for different numbers of Born–Oppenheimer potentials and vibronic wave packets on a full 3-dimensional (two electron coordinates plus one nuclear coordinate) grid. Using strong fields, we show that it is possible to dynamically lock the spin state of the system by decoupling the singlet–triplet transition via a nonresonant dynamic Stark effect in the adiabatic limit. Although a similar spin-locking mechanism is observed in the dynamics of vibronic wave packets, multiphoton ionization cannot be neglected leading to the breakdown of the control scheme.}, author = {Falge, Mirjam and Engel, Volker and Lein, Manfred and Vindel-Zandbergen, Patricia and Chang, Bo Y. and Sola, Ignacio R.}, journal = {The Journal of Physical Chemistry A}, keywords = {ak-engel}, note = {PMID: 22946899}, number = 46, pages = {11427-11433}, title = {Quantum Wave-Packet Dynamics in Spin-Coupled Vibronic States}, volume = 116, year = 2012 }

• Foldamer with a spiral perylene bisimide staircase aggregate structure. Dehm, Volker; Buchner, Michael; Seibt, Joachim; Engel, Volker; Wurthner, Frank. In Chem. Sci., 2(11), S. 2094–2100. The Royal Society of Chemistry, 2011.
  • [ BibTeX ]
  • [ DOI ]
  @article{C1SC00435B, abstract = {Although the precise control of dye-dye interactions is known to be of fundamental importance to achieve desired functional properties in [small pi]-conjugated materials{,} there are only sporadic examples where precise structural control of dye-dye interactions could be achieved by the attachment of the chromophores to an oligomeric or polymeric backbone. In this edge article{,} we introduce an oligophenylene ethynylene/perylene bisimide (PBI) dye system which is conceived by the foldamer concept. The molecular design enables folding of the [small pi]-conjugated oligomer to give a geometrically well-defined [small pi]-stack of intrastrand PBI molecules. The synthesis of the foldamer and its characterization by MALDI-TOF mass spectrometry are described{,} and the average size is estimated by gel permeation chromatography (GPC) and diffusion ordered NMR spectroscopy (DOSY). The folding dynamics are demonstrated by ultraviolet/visible absorption and fluorescence emission spectroscopic studies as the folded and unfolded states possess distinct optical properties. Quantum dynamic considerations revealed a good agreement of the calculated aggregate absorption spectrum with those obtained experimentally.}, author = {Dehm, Volker and Buchner, Michael and Seibt, Joachim and Engel, Volker and Wurthner, Frank}, journal = {Chem. Sci.}, keywords = {ak-engel}, number = 11, pages = {2094-2100}, publisher = {The Royal Society of Chemistry}, title = {Foldamer with a spiral perylene bisimide staircase aggregate structure}, volume = 2, year = 2011 }
• Time-resolved photoelectron spectroscopy of coupled electron-nuclear motion. Falge, Mirjam; Engel, Volker; Gräfe, Stefanie. In The Journal of Chemical Physics, 134(18), S. 184307. {AIP} Publishing, 2011.
  • [ BibTeX ]
  • [ DOI ]
  @article{Falge_2011, author = {Falge, Mirjam and Engel, Volker and Gräfe, Stefanie}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {05}, number = 18, pages = 184307, publisher = {{AIP} Publishing}, title = {Time-resolved photoelectron spectroscopy of coupled electron-nuclear motion}, volume = 134, year = 2011 }
• Interference in above-threshold-ionization electron distributions from molecules. Henkel, Jost; Lein, Manfred; Engel, Volker. In Phys. Rev. A, 83(5), S. 051401. American Physical Society, 2011.
  • [ BibTeX ]
  • [ DOI ]
  @article{PhysRevA.83.051401, author = {Henkel, Jost and Lein, Manfred and Engel, Volker}, journal = {Phys. Rev. A}, keywords = {ak-engel}, month = {05}, number = 5, pages = {051401}, publisher = {American Physical Society}, title = {Interference in above-threshold-ionization electron distributions from molecules}, volume = 83, year = 2011 }
• Interference Effects in Vibronic 2D-Spectra of Diatomic Molecules. Schubert, Alexander; Engel, Volker. In Zeitschrift f{ü}r Physikalische Chemie, 225(6-7), S. 703–714. Walter de Gruyter {GmbH}, 2011.
  • [ BibTeX ]
  • [ DOI ]
  @article{Schubert2011, author = {Schubert, Alexander and Engel, Volker}, journal = {Zeitschrift f\"{u}r Physikalische Chemie}, keywords = {ak-engel}, month = {07}, number = {6-7}, pages = {703–714}, publisher = {Walter de Gruyter {GmbH}}, title = {Interference Effects in Vibronic 2D-Spectra of Diatomic Molecules}, volume = 225, year = 2011 }
• Two-dimensional vibronic spectroscopy of coherent wave-packet motion. Schubert, Alexander; Engel, Volker. In The Journal of Chemical Physics, 134(10), S. 104304. {AIP} Publishing, 2011.
  • [ BibTeX ]
  • [ DOI ]
  @article{Schubert_2011, author = {Schubert, Alexander and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {03}, number = 10, pages = 104304, publisher = {{AIP} Publishing}, title = {Two-dimensional vibronic spectroscopy of coherent wave-packet motion}, volume = 134, year = 2011 }
• Nuclear and electronic momentum distributions from pulse induced photodissociation. Hader, Kilian; Engel, Volker. In Chemical Physics Letters, 509(4), S. 119–123. 2011.
  • [ BibTeX ]
  • [ DOI ]
  @article{HADER2011119, author = {Hader, Kilian and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 4, pages = {119 - 123}, title = {Nuclear and electronic momentum distributions from pulse induced photodissociation}, volume = 509, year = 2011 }

• Vibrational-state and isotope dependence of high-order harmonic generation in water molecules. Falge, Mirjam; Engel, Volker; Lein, Manfred. In Phys. Rev. A, 81(2), S. 023412. American Physical Society, 2010.
  • [ BibTeX ]
  • [ DOI ]
  @article{PhysRevA.81.023412, author = {Falge, Mirjam and Engel, Volker and Lein, Manfred}, journal = {Phys. Rev. A}, keywords = {ak-engel}, month = {02}, number = 2, pages = {023412}, publisher = {American Physical Society}, title = {Vibrational-state and isotope dependence of high-order harmonic generation in water molecules}, volume = 81, year = 2010 }
• Mapping of quantum phases by two-dimensional vibronic spectroscopy of wave-packet revivals. Schubert, Alexander; Renziehausen, Klaus; Engel, Volker. In Phys. Rev. A, 82(1), S. 013419. American Physical Society, 2010.
  • [ BibTeX ]
  • [ DOI ]
  @article{PhysRevA.82.013419, author = {Schubert, Alexander and Renziehausen, Klaus and Engel, Volker}, journal = {Phys. Rev. A}, keywords = {ak-engel}, month = {07}, number = 1, pages = {013419}, publisher = {American Physical Society}, title = {Mapping of quantum phases by two-dimensional vibronic spectroscopy of wave-packet revivals}, volume = 82, year = 2010 }
• Dissipative Wave Packet Dynamics of Hydrophobic → Hydrophilic Site Switching in Phenol-Ar Clusters. Walter, Ch.; Kritzer, R.; Schubert, A.; Meier, C.; Dopfer, O.; Engel, V. In The Journal of Physical Chemistry A, 114(36), S. 9743–9748. 2010.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jp101964e, abstract = {We analyze the results of recent pump−probe experiments on the site-switching dynamics of Ar within cationic phenol-Ar2 clusters. A reaction-path model is employed for the wave packet dynamics. It is shown that the mechanism of energy dissipation is to be included to understand the features of the transient signals. Therefore, a simple recipe to include energy relaxation to the quantum dynamics is introduced. It is then possible to reproduce the measured pump−probe signals by adjustment of only two parameters.}, author = {Walter, Ch. and Kritzer, R. and Schubert, A. and Meier, C. and Dopfer, O. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {ak-engel}, note = {PMID: 20433178}, number = 36, pages = {9743-9748}, title = {Dissipative Wave Packet Dynamics of Hydrophobic → Hydrophilic Site Switching in Phenol-Ar Clusters}, volume = 114, year = 2010 }

• Local control of population transfer in molecules under fluctuating perturbations. Kritzer, R.; Meier, C.; Engel, Volker. In Chemical Physics Letters, 477(1), S. 75–79. 2009.
  • [ BibTeX ]
  • [ DOI ]
  @article{KRITZER200975, author = {Kritzer, R. and Meier, C. and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 1, pages = {75 - 79}, title = {Local control of population transfer in molecules under fluctuating perturbations}, volume = 477, year = 2009 }
• Probing the geometry dependence of molecular dimers with two-dimensional-vibronic spectroscopy. Seibt, Joachim; Renziehausen, Klaus; Voronine, Dmitri V.; Engel, Volker. In The Journal of Chemical Physics, 130(13), S. 134318. {AIP} Publishing, 2009.
  • [ BibTeX ]
  • [ DOI ]
  @article{Seibt_2009, author = {Seibt, Joachim and Renziehausen, Klaus and Voronine, Dmitri V. and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {04}, number = 13, pages = 134318, publisher = {{AIP} Publishing}, title = {Probing the geometry dependence of molecular dimers with two-dimensional-vibronic spectroscopy}, volume = 130, year = 2009 }
• Vibronic Transitions and Quantum Dynamics in Molecular Oligomers: A Theoretical Analysis with an Application to Aggregates of Perylene Bisimides. Seibt, J.; Winkler, T.; Renziehausen, K.; Dehm, V.; Würthner, F.; Meyer, H.-D.; Engel, V. In The Journal of Physical Chemistry A, 113(48), S. 13475–13482. 2009.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jp904892v, abstract = {Vibronic absorption spectra of molecular aggregates consisting of up to N = 9 monomer units are calculated employing methods of time-dependent quantum mechanics. Taking one vibrational degree of freedom for each monomer into account and treating one-exciton excited electronic states leads to a problem with N vibrations and N electronically coupled states. The demanding quantum propagation is carried out within the multiconfiguration time-depended Hartree method (MCTDH). Spectral features of and population transfer in the aggregates are analyzed as a function of the aggregate size and the strength of the electronic coupling. With a model for oligomers of perylene bisimides, it is shown how measured temperature-dependent absorption spectra correlate with the aggregate size. Furthermore, the exciton localization and dynamics in these aggregates are investigated.}, author = {Seibt, J. and Winkler, T. and Renziehausen, K. and Dehm, V. and Würthner, F. and Meyer, H.-D. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {ak-engel}, note = {PMID: 19831416}, number = 48, pages = {13475-13482}, title = {Vibronic Transitions and Quantum Dynamics in Molecular Oligomers: A Theoretical Analysis with an Application to Aggregates of Perylene Bisimides}, volume = 113, year = 2009 }
• On the divergence of time-dependent perturbation theory applied to laser-induced molecular transitions. Renziehausen, Klaus; Marquetand, Philipp; Engel, Volker. In Journal of Physics B: Atomic, Molecular and Optical Physics, 42(19), S. 195402. 2009.
  • [ BibTeX ]
  @article{0953-4075-42-19-195402, abstract = {Population transfer between electronic molecular states can be effectively induced via the interaction with shaped laser pulses. Regarding a numerical example, it is demonstrated that perturbation theory, as is often applied in numerical simulations of field-matter interactions, might lead to divergences. The occurring error accumulating in the norm of the wavefunction can be decomposed into two contributions. The first one is a small numerical error, which is controllable by minimization of the time-propagation step, whereas the second one is related to the order of the perturbative expansion. These two contributions behave differently upon variations of the potential energy surface of the system and also the laser pulse parameters. An improved scheme is proposed in which the first part carrying the numerical error disappears.}, author = {Renziehausen, Klaus and Marquetand, Philipp and Engel, Volker}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, keywords = {ak-engel}, number = 19, pages = 195402, title = {On the divergence of time-dependent perturbation theory applied to laser-induced molecular transitions}, volume = 42, year = 2009 }

• Absorption and emission spectroscopy of molecular trimers: Cyclic versus linear geometries. Seibt, Joachim; Engel, Volker. In Chemical Physics, 347(1), S. 120–126. 2008.
  • [ BibTeX ]
  • [ DOI ]
  @article{SEIBT2008120, author = {Seibt, Joachim and Engel, Volker}, journal = {Chemical Physics}, keywords = {ak-engel}, note = {Ultrafast Photoinduced Processes in Polyatomic Molecules}, number = 1, pages = {120 - 126}, title = {Absorption and emission spectroscopy of molecular trimers: Cyclic versus linear geometries}, volume = 347, year = 2008 }
• Analysis of laser fields for photoassociation and molecular stabilization derived from local control theory. Marquetand, P; Engel, V. In Journal of Physics B: Atomic, Molecular and Optical Physics, 41(7), S. 074026. 2008.
  • [ BibTeX ]
  @article{0953-4075-41-7-074026, abstract = {Laser control fields are derived within local control theory (LCT) to achieve molecular photoassociation and successive vibrational stabilization. This approach allows for a straightforward interpretation of the field properties, as the control field is constructed from the dynamics of the system. Model calculations on the ground-state collision of H + F atoms are carried out. The corresponding fields are analysed and it is shown that their time dependence can be understood in every respect.}, author = {Marquetand, P and Engel, V}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, keywords = {ak-engel}, number = 7, pages = {074026}, title = {Analysis of laser fields for photoassociation and molecular stabilization derived from local control theory}, volume = 41, year = 2008 }
• Molecular dump processes induced by chirped laser pulses. Marquetand, Philipp; Nuernberger, Patrick; Brixner, Tobias; Engel, Volker. In The Journal of Chemical Physics, 129(7), S. 074303. {AIP} Publishing, 2008.
  • [ BibTeX ]
  • [ DOI ]
  @article{Marquetand_2008, author = {Marquetand, Philipp and Nuernberger, Patrick and Brixner, Tobias and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {08}, number = 7, pages = {074303}, publisher = {{AIP} Publishing}, title = {Molecular dump processes induced by chirped laser pulses}, volume = 129, year = 2008 }
• Circular dichroism spectroscopy of small molecular aggregates: Dynamical features and size effects. Seibt, Joachim; Dehm, Volker; Würthner, Frank; Engel, Volker. In The Journal of Chemical Physics, 128(20), S. 204303. {AIP} Publishing, 2008.
  • [ BibTeX ]
  • [ DOI ]
  @article{Seibt_2008, author = {Seibt, Joachim and Dehm, Volker and Würthner, Frank and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {05}, number = 20, pages = 204303, publisher = {{AIP} Publishing}, title = {Circular dichroism spectroscopy of small molecular aggregates: Dynamical features and size effects}, volume = 128, year = 2008 }
• Quantum Study of the Absorption Spectroscopy of Bis(triarylamine) Radical Cations. Seibt, J.; Schaumlöffel, A.; Lambert, C.; Engel, V. In The Journal of Physical Chemistry A, 112(41), S. 10178–10184. 2008.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jp804779s, abstract = {Absorption spectra of bridged triarylamine radical cations are calculated quantum mechanically which extends our previous classical analysis (Lambert et al. J. Phys. Chem. A 2004, 108, 6474). A comparison between spectra determined within a diabatic and an adiabatic representation shows that under certain circumstances deviations occur. It is found that the latter are mainly caused by the Condon approximation for the dipole moments. The inclusion of vibrational degrees of freedom leads to an excellent agreement with experiment.}, author = {Seibt, J. and Schaumlöffel, A. and Lambert, C. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {ak-engel}, note = {PMID: 18811125}, number = 41, pages = {10178-10184}, title = {Quantum Study of the Absorption Spectroscopy of Bis(triarylamine) Radical Cations}, volume = 112, year = 2008 }
• Exciton Trapping in π-Conjugated Materials: A Quantum-Chemistry-Based Protocol Applied to Perylene Bisimide Dye Aggregates. Fink, Reinhold F.; Seibt, Joachim; Engel, Volker; Renz, Manuel; Kaupp, Martin; Lochbrunner, Stefan; Zhao, Hong-Mei; Pfister, Johannes; Würthner, Frank; Engels, Bernd. In Journal of the American Chemical Society, 130(39), S. 12858–12859. 2008.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/ja804331b, abstract = {Access to excited-state structures and dynamics of π-chromophor aggregates is needed to understand their fluorescence behavior and the properties of related materials. A quantum-chemistry-based protocol that provides quantitative and qualitative insight into fluorescence spectra has been applied to perylene bisimide dimers and provides excellent agreement with measured fluorescence spectra. Both dispersion and dipol−dipole interactions determine the preferred relative arrangements of the chromophores in ground and excited states of the dimer. An exciton trappping mechanism is identified, which may limit the energy transfer properties of perylene bisimide and other dye materials.}, author = {Fink, Reinhold F. and Seibt, Joachim and Engel, Volker and Renz, Manuel and Kaupp, Martin and Lochbrunner, Stefan and Zhao, Hong-Mei and Pfister, Johannes and Würthner, Frank and Engels, Bernd}, journal = {Journal of the American Chemical Society}, keywords = {ak-engel}, note = {PMID: 18767851}, number = 39, pages = {12858-12859}, title = {Exciton Trapping in π-Conjugated Materials: A Quantum-Chemistry-Based Protocol Applied to Perylene Bisimide Dye Aggregates}, volume = 130, year = 2008 }
• Attosecond Photoelectron Spectroscopy of Electron Tunneling in a Dissociating Hydrogen Molecular Ion. Gräfe, Stefanie; Engel, Volker; Ivanov, Misha Yu. In Phys. Rev. Lett., 101(10), S. 103001. American Physical Society, 2008.
  • [ BibTeX ]
  • [ DOI ]
  @article{PhysRevLett.101.103001, author = {Gr\"afe, Stefanie and Engel, Volker and Ivanov, Misha Yu.}, journal = {Phys. Rev. Lett.}, keywords = {ak-engel}, month = {09}, number = 10, pages = 103001, publisher = {American Physical Society}, title = {Attosecond Photoelectron Spectroscopy of Electron Tunneling in a Dissociating Hydrogen Molecular Ion}, volume = 101, year = 2008 }
• On the inversion of geometric parameters from absorption and circular dichroism spectroscopy of molecular dimers. Eisfeld, Alexander; Seibt, Joachim; Engel, Volker. In Chemical Physics Letters, 467(1), S. 186–190. 2008.
  • [ BibTeX ]
  • [ DOI ]
  @article{EISFELD2008186, author = {Eisfeld, Alexander and Seibt, Joachim and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 1, pages = {186 - 190}, title = {On the inversion of geometric parameters from absorption and circular dichroism spectroscopy of molecular dimers}, volume = 467, year = 2008 }

• On the calculation of circular dichroism spectra using quantum wave-packet dynamics with an application to molecular dimers. Seibt, Joachim; Engel, Volker. In The Journal of Chemical Physics, 126(7), S. 074110. {AIP} Publishing, 2007.
  • [ BibTeX ]
  • [ DOI ]
  @article{Seibt_2007, author = {Seibt, Joachim and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {02}, number = 7, pages = {074110}, publisher = {{AIP} Publishing}, title = {On the calculation of circular dichroism spectra using quantum wave-packet dynamics with an application to molecular dimers}, volume = 126, year = 2007 }
• Properties of wave packets deduced from quantum control fitness landscapes. Marquetand, P.; Nuernberger, P.; Vogt, G.; Brixner, T.; Engel, V. In EPL (Europhysics Letters), 80(5), S. 53001. 2007.
  • [ BibTeX ]
  @article{0295-5075-80-5-53001, abstract = {We demonstrate the versatility of shaped femtosecond dump pulses for the investigation of molecular quantum systems. Model calculations show that population is most efficiently transferred by shaped pulses. Illustrative fitness landscapes, where the excited-state population is analyzed as a function of selected laser pulse parameters, facilitate a characterization of wave packet evolution and the potential energy surfaces. A first experimental implementation is presented for retinal photoisomerization in bacteriorhodopsin.}, author = {Marquetand, P. and Nuernberger, P. and Vogt, G. and Brixner, T. and Engel, V.}, journal = {EPL (Europhysics Letters)}, keywords = {ak-engel}, number = 5, pages = 53001, title = {Properties of wave packets deduced from quantum control fitness landscapes}, volume = 80, year = 2007 }
• Strong-field dressing of vibrational manifolds within ultrafast coherent Raman excitation. Gräfe, Stefanie; Akimov, Denis A.; Böhm, Belinda; Zheltikov, Aleksei M.; Scully, Marlan O.; Kiefer, Wolfgang; Engel, Volker; Siebert, Torsten. In Journal of Raman Spectroscopy, 38(8), S. 998–1005. John Wiley & Sons, Ltd., 2007.
  • [ BibTeX ]
  • [ DOI ]
  @article{JRS:JRS1720, abstract = {The mechanism of ultrafast, coherent Raman transitions driven at high field strengths is explored in theory and experiment. The study addresses the possibility of maintaining control of a vibrational wavepacket that is guided to a desired final state during the course of a Raman excitation by significantly perturbing the participating molecular states on the time scale of the dynamics under manipulation. Variations in the sequence and amplitude of the pulsed laser fields give direct insight into the nature of the perturbation as well as the population flow within vibrational manifolds of the electronic states involved in the transition. The excitation scheme realized in this work demonstrates control over the dynamics of a molecular system through a non-adiabatic pathway that utilizes the full manifold of dressed states induced by the laser fields driving the transition rather than isolating the system in a decoupled dressed state common for the adiabatic passage scheme. By preparing highly excited virbrational states in molecular iodine with this scheme, it is shown that a vibrational wavepacket can be steered by controlling the phase with which the character of the field-free states is introduced into the manifold of dressed states participating in the transition. This scheme seeks to open the possibility of using ultrafast Raman excitation for initiating and observing chemical reactions in the electronic ground state of a molecular system. Copyright © 2007 John Wiley & Sons, Ltd.}, author = {Gräfe, Stefanie and Akimov, Denis A. and Böhm, Belinda and Zheltikov, Aleksei M. and Scully, Marlan O. and Kiefer, Wolfgang and Engel, Volker and Siebert, Torsten}, journal = {Journal of Raman Spectroscopy}, keywords = {ak-engel}, number = 8, pages = {998–1005}, publisher = {John Wiley & Sons, Ltd.}, title = {Strong-field dressing of vibrational manifolds within ultrafast coherent Raman excitation}, volume = 38, year = 2007 }
• Wave-packet dynamics in molecular dimers. Seibt, Joachim; Engel, Volker. In Chemical Physics, 338(2), S. 143–149. 2007.
  • [ BibTeX ]
  • [ DOI ]
  @article{SEIBT2007143, author = {Seibt, Joachim and Engel, Volker}, journal = {Chemical Physics}, keywords = {ak-engel}, note = {Molecular Wave Packet Dynamics}, number = 2, pages = {143 - 149}, title = {Wave-packet dynamics in molecular dimers}, volume = 338, year = 2007 }
• Photoluminescence and Conductivity of Self-Assembled π–π Stacks of Perylene Bisimide Dyes. Chen, Zhijian; Stepanenko, Vladimir; Dehm, Volker; Prins, Paulette; Siebbeles, Laurens D. A.; Seibt, Joachim; Marquetand, Philipp; Engel, Volker; Würthner, Frank. In Chemistry – A European Journal, 13(2), S. 436–449. WILEY-VCH Verlag, 2007.
  • [ BibTeX ]
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  @article{CHEM:CHEM200600889, abstract = {The self-assembly of a new, highly fluorescent perylene bisimide dye 2 into π stacks, both in solution and condensed phase, has been studied in detail by NMR spectroscopy, vapor pressure osmometry (VPO), UV/Vis and fluorescence spectroscopy, differential scanning calorimetry (DSC), optical polarizing microscopy (OPM) and X-ray diffraction. The NMR and VPO measurements revealed the formation of extended π–π stacks of the dye molecules in solution. The aggregate size determined from VPO and DOSY NMR measurements agree well with that obtained from the concentration and temperature-dependent UV/Vis spectral data by employing the isodesmic model (equal K model). In the condensed state, dye 2 possesses a hexagonal columnar liquid crystalline (LC) phase as confirmed by X-ray diffraction analysis. The columnar stacking of this dye has been further explored by atomic force microscopy (AFM). Well-resolved columnar nanostructures of the compound are observed on graphite surface. A color-tunable luminescence from green to red has been observed upon aggregation which is accompanied by an increase of the fluorescence lifetime and depolarization. The observed absorption properties can be explained in terms of molecular exciton theory. The charge transport properties of dye 2 have been investigated by pulse radiolysis-time resolved microwave conductivity measurements and a 1D charge carrier mobility up to 0.42 cm2 V−1 s−1 is obtained. Considering the promising self-assembly, semiconducting, and luminescence properties of this dye, it might serve as a useful functional material for nano(opto)electronics.}, author = {Chen, Zhijian and Stepanenko, Vladimir and Dehm, Volker and Prins, Paulette and Siebbeles, Laurens D. A. and Seibt, Joachim and Marquetand, Philipp and Engel, Volker and Würthner, Frank}, journal = {Chemistry – A European Journal}, keywords = {ak-engel}, number = 2, pages = {436–449}, publisher = {WILEY-VCH Verlag}, title = {Photoluminescence and Conductivity of Self-Assembled π–π Stacks of Perylene Bisimide Dyes}, volume = 13, year = 2007 }
• Circular dichroism and absorption spectroscopy of merocyanine dimer aggregates: molecular properties and exciton transfer dynamics from time-dependent quantum calculations. Seibt, Joachim; Lohr, Andreas; Wurthner, Frank; Engel, Volker. In Phys. Chem. Chem. Phys., 9(47), S. 6214–6218. The Royal Society of Chemistry, 2007.
  • [ BibTeX ]
  • [ DOI ]
  @article{B712155E, abstract = {A wave packet approach to the calculation and interpretation of circular dichroism (CD) spectra is applied to the spectroscopy of aggregates of a merocyanine dye. A combined analysis of absorption and CD spectra allows for the extraction of geometric information and excited state electronic coupling. It is shown that in the case of dimer aggregates of a chiral merocyanine dye{,} it is possible to infer the dynamics of an exciton transfer directly from the CD spectrum. This relation is established via the Fourier relation to a time-dependent correlation function reflecting the quantum dynamics in the dye aggregate.}, author = {Seibt, Joachim and Lohr, Andreas and Wurthner, Frank and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 47, pages = {6214-6218}, publisher = {The Royal Society of Chemistry}, title = {Circular dichroism and absorption spectroscopy of merocyanine dimer aggregates: molecular properties and exciton transfer dynamics from time-dependent quantum calculations}, volume = 9, year = 2007 }
• Local control theory applied to molecular photoassociation. Marquetand, Philipp; Engel, Volker. In The Journal of Chemical Physics, 127(8), S. 084115. {AIP} Publishing, 2007.
  • [ BibTeX ]
  • [ DOI ]
  @article{Marquetand_2007, author = {Marquetand, Philipp and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {08}, number = 8, pages = {084115}, publisher = {{AIP} Publishing}, title = {Local control theory applied to molecular photoassociation}, volume = 127, year = 2007 }
• On the limitations of adiabatic population transfer between molecular electronic states induced by intense femtosecond laser pulses. Gräfe, S.; Kiefer, W.; Engel, V. In The Journal of Chemical Physics, 127(13), S. 134306. {AIP} Publishing, 2007.
  • [ BibTeX ]
  • [ DOI ]
  @article{Gr_fe_2007, author = {Gräfe, S. and Kiefer, W. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = 10, number = 13, pages = 134306, publisher = {{AIP} Publishing}, title = {On the limitations of adiabatic population transfer between molecular electronic states induced by intense femtosecond laser pulses}, volume = 127, year = 2007 }
• Absorption spectroscopy of molecular trimers. Seibt, Joachim; Dehm, Volker; Würthner, Frank; Engel, Volker. In The Journal of Chemical Physics, 126(16), S. 164308. {AIP} Publishing, 2007.
  • [ BibTeX ]
  • [ DOI ]
  @article{Seibt_2007, author = {Seibt, Joachim and Dehm, Volker and Würthner, Frank and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {04}, number = 16, pages = 164308, publisher = {{AIP} Publishing}, title = {Absorption spectroscopy of molecular trimers}, volume = 126, year = 2007 }

• Classical aspects emerging from local control of energy and particle transfer in molecules. Gräfe, Stefanie; Marquetand, Philipp; Engel, Volker. In Journal of Photochemistry and Photobiology A: Chemistry, 180(3), S. 271–276. 2006.
  • [ BibTeX ]
  • [ DOI ]
  @article{GRAFE2006271, author = {Gräfe, Stefanie and Marquetand, Philipp and Engel, Volker}, journal = {Journal of Photochemistry and Photobiology A: Chemistry}, keywords = {Coherent}, note = {Coherent Control of Photochemical and Photobiological Processes}, number = 3, pages = {271 - 276}, title = {Classical aspects emerging from local control of energy and particle transfer in molecules}, volume = 180, year = 2006 }
• The excited-state geometry of 1-hydroxy-2- acetonaphthone: a resonance Raman and quantum chemical study. Szeghalmi, A. V.; Engel, V.; Zgierski, M. Z.; Popp, J.; Schmitt, M. In Journal of Raman Spectroscopy, 37(1-3), S. 148–160. John Wiley & Sons, Ltd., 2006.
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  • [ DOI ]
  @article{JRS:JRS1449, abstract = {1-Hydroxy-2-acetonaphthone (HAN), an intramolecular proton transfer system, was investigated in the present study by means of quantum chemical calculations and resonance Raman spectroscopy. To determine the Franck–Condon parameters, a time-dependent approach for the analysis of the resonance Raman spectra was applied. About 18 vibrational modes were found to be involved in the initial dynamics of HAN upon photo excitation. Moreover, the excited-state geometry of HAN was optimized at the CASSCF level of theory and the displacement parameters were determined. A very good agreement between the theoretical and experimentally derived parameters was obtained. The vibrations with the highest displacements correspond to stretching and in-plane deformation modes of the naphthalene ring and the conjugated carbonyl group, while the OH stretching mode exhibits no observable enhancement. Hence, a general molecular rearrangement takes place upon photo excitation, where the intramolecular oxygen–oxygen distance reduces corresponding to a redistribution of the electron density. Copyright © 2006 John Wiley & Sons, Ltd.}, author = {Szeghalmi, A. V. and Engel, V. and Zgierski, M. Z. and Popp, J. and Schmitt, M.}, journal = {Journal of Raman Spectroscopy}, keywords = {ak-engel}, number = {1-3}, pages = {148–160}, publisher = {John Wiley & Sons, Ltd.}, title = {The excited-state geometry of 1-hydroxy-2- acetonaphthone: a resonance Raman and quantum chemical study}, volume = 37, year = 2006 }
• Application of a reflection principle to spectroscopic transitions in molecular dimers. Koller, Stephan; Seibt, Joachim; Marquetand, Philipp; Engel, Volker. In Chemical Physics Letters, 433(1), S. 199–203. 2006.
  • [ BibTeX ]
  • [ DOI ]
  @article{KOLLER2006199, author = {Koller, Stephan and Seibt, Joachim and Marquetand, Philipp and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 1, pages = {199 - 203}, title = {Application of a reflection principle to spectroscopic transitions in molecular dimers}, volume = 433, year = 2006 }
• Ground state vibrational wave-packet and recovery dynamics studied by time-resolved CARS and pump-CARS spectroscopy. Siebert, T.; Schmitt, M.; Gräfe, S.; Engel, Volker. In Journal of Raman Spectroscopy, 37(1-3), S. 397–403. John Wiley & Sons, Ltd., 2006.
  • [ BibTeX ]
  • [ DOI ]
  @article{JRS:JRS1441, abstract = {Recent experiments on gaseous iodine and β-carotene are analyzed within a wave-packet description of femtosecond-time resolved four-wave mixing spectroscopy. Employing the same formalism, two different experimental setups, both established in the Kiefer group, are treated. In a transient four-wave-mixing (FWM) experiment, where two pulses interact simultaneously with the system, the interaction with a third time-delayed pulse leads to light emission reflecting ground state vibrational dynamics in I2. On the other hand, delaying a FWM-pulse sequence with respect to a single pump pulse interacting with β-carotene yields a signal that is directly proportional to the population of a selected nuclear eigenstate in the electronic ground state. Thus, within this setup, it is possible to monitor ground-state re-population dynamics mode specifically. Copyright © 2006 John Wiley & Sons, Ltd.}, author = {Siebert, T. and Schmitt, M. and Gräfe, S. and Engel, Volker}, journal = {Journal of Raman Spectroscopy}, keywords = {ak-engel}, number = {1-3}, pages = {397–403}, publisher = {John Wiley & Sons, Ltd.}, title = {Ground state vibrational wave-packet and recovery dynamics studied by time-resolved CARS and pump-CARS spectroscopy}, volume = 37, year = 2006 }
• Local control theory applied to coupled electronic and nuclear motion. Gräfe, Stefanie; Engel, Volker. In Chemical Physics, 329(1), S. 118–125. 2006.
  • [ BibTeX ]
  • [ DOI ]
  @article{GRAFE2006118, author = {Gräfe, Stefanie and Engel, Volker}, journal = {Chemical Physics}, keywords = {ak-engel}, note = {Electron Correlation and Multimode Dynamics in Molecules}, number = 1, pages = {118 - 125}, title = {Local control theory applied to coupled electronic and nuclear motion}, volume = 329, year = 2006 }
• Local control of the quantum dynamics in multiple potential wells. Marquetand, Philipp; Gräfe, Stefanie; Scheidel, Daniel; Engel, Volker. In The Journal of Chemical Physics, 124(5), S. 054325. {AIP} Publishing, 2006.
  • [ BibTeX ]
  • [ DOI ]
  @article{Marquetand_2006, author = {Marquetand, Philipp and Gräfe, Stefanie and Scheidel, Daniel and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {02}, number = 5, pages = {054325}, publisher = {{AIP} Publishing}, title = {Local control of the quantum dynamics in multiple potential wells}, volume = 124, year = 2006 }
• On the geometry dependence of molecular dimer spectra with an application to aggregates of perylene bisimide. Seibt, J.; Marquetand, P.; Engel, Volker; Chen, Z.; Dehm, V.; Würthner, F. In Chemical Physics, 328(1), S. 354–362. 2006.
  • [ BibTeX ]
  • [ DOI ]
  @article{SEIBT2006354, author = {Seibt, J. and Marquetand, P. and Engel, Volker and Chen, Z. and Dehm, V. and Würthner, F.}, journal = {Chemical Physics}, keywords = {Optical}, number = 1, pages = {354 - 362}, title = {On the geometry dependence of molecular dimer spectra with an application to aggregates of perylene bisimide}, volume = 328, year = 2006 }
• Complete local control of molecular excited state photo-fragmentation. Marquetand, Philipp; Engel, Volker. In Chemical Physics Letters, 426(4), S. 263–267. 2006.
  • [ BibTeX ]
  • [ DOI ]
  @article{MARQUETAND2006263, author = {Marquetand, Philipp and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 4, pages = {263 - 267}, title = {Complete local control of molecular excited state photo-fragmentation}, volume = 426, year = 2006 }

• Predissociation and dissociation dynamics in quantum control fields. Marquetand, Philipp; Engel, Volker. In Chemical Physics Letters, 407(4), S. 471–476. 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{MARQUETAND2005471, author = {Marquetand, Philipp and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 4, pages = {471 - 476}, title = {Predissociation and dissociation dynamics in quantum control fields}, volume = 407, year = 2005 }
• Instantaneous dynamics and quantum control fields: Principle and numerical applications. Gräfe, S.; Meier, C.; Engel, V. In The Journal of Chemical Physics, 122(18), S. 184103. {AIP} Publishing, 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{Gr_fe_2005, author = {Gräfe, S. and Meier, C. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {05}, number = 18, pages = 184103, publisher = {{AIP} Publishing}, title = {Instantaneous dynamics and quantum control fields: Principle and numerical applications}, volume = 122, year = 2005 }
• Population transfer in the multiphoton excitation of molecules. Gräfe, S.; Erdmann, M.; Engel, V. In Phys. Rev. A, 72(1), S. 013404. American Physical Society, 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{PhysRevA.72.013404, author = {Gr\"afe, S. and Erdmann, M. and Engel, V.}, journal = {Phys. Rev. A}, keywords = {ak-engel}, month = {07}, number = 1, pages = {013404}, publisher = {American Physical Society}, title = {Population transfer in the multiphoton excitation of molecules}, volume = 72, year = 2005 }
• Local control of molecular fragmentation: The role of orientation. Marquetand, Philipp; Meier, Christoph; Engel, Volker. In The Journal of Chemical Physics, 123(20), S. 204320. {AIP} Publishing, 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{Marquetand_2005, author = {Marquetand, Philipp and Meier, Christoph and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = 11, number = 20, pages = 204320, publisher = {{AIP} Publishing}, title = {Local control of molecular fragmentation: The role of orientation}, volume = 123, year = 2005 }
• Isotope effects in the photofragmentation of symmetric molecules: The branching ratio of {OD}∕{OH} in water. Henriksen, Niels E.; M{\o}ller, Klaus B.; Engel, Volker. In The Journal of Chemical Physics, 122(20), S. 204320. {AIP} Publishing, 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{Henriksen_2005, author = {Henriksen, Niels E. and M{\o}ller, Klaus B. and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {05}, number = 20, pages = 204320, publisher = {{AIP} Publishing}, title = {Isotope effects in the photofragmentation of symmetric molecules: The branching ratio of {OD}∕{OH} in water}, volume = 122, year = 2005 }
• FEMTOSECOND LASER PHOTOELECTRON SPECTROSCOPY ON ATOMS AND SMALL MOLECULES: Prototype Studies in Quantum Control. Wollenhaupt, M.; Engel, V.; Baumert, T. In Annual Review of Physical Chemistry, 56(1), S. 25–56. 2005.
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  • [ DOI ]
  @article{doi:10.1146/annurev.physchem.56.092503.141315, abstract = {▪ Abstract We review prototype studies in the area of quantum control with femtosecond lasers. We restrict this discussion to atoms and diatomics under gas-phase collision-free conditions to allow for a comparison between theory and experiment. Both the perturbative regime and the nonperturbative regime of the light-matter interaction are addressed. To that end, atomic/molecular beam techniques are combined together with femtosecond laser techniques and energy-resolved photoelectron spectroscopy and ion detection. Highly detailed information on the laser-induced quantum dynamics is extracted with the help of kinetic energy-resolved photoelectron spectroscopy.}, author = {Wollenhaupt, M. and Engel, V. and Baumert, T.}, journal = {Annual Review of Physical Chemistry}, keywords = {ak-engel}, note = {PMID: 15796695}, number = 1, pages = {25-56}, title = {FEMTOSECOND LASER PHOTOELECTRON SPECTROSCOPY ON ATOMS AND SMALL MOLECULES: Prototype Studies in Quantum Control}, volume = 56, year = 2005 }
• Femtosecond pulse induced predissociation dynamics in static electric fields. Marquetand, P.; Engel, V. In Phys. Chem. Chem. Phys., 7(3), S. 469–474. The Royal Society of Chemistry, 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{B415885G, abstract = {The quantum dynamics of NaI molecules in static electric fields is investigated. Upon femtosecond excitation{,} a wave packet is prepared which performs a quasi-bound motion in a coupled system of two electronic states. A detailed study of the influence of the external field on the molecular orientation on one hand{,} and the interplay between the rotational{,} vibrational and predissociation dynamics on the other{,} is presented. It is documented that polarization dependent pump-probe experiments are a powerful tool to follow the orientational dynamics in real time.}, author = {Marquetand, P. and Engel, V.}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 3, pages = {469-474}, publisher = {The Royal Society of Chemistry}, title = {Femtosecond pulse induced predissociation dynamics in static electric fields}, volume = 7, year = 2005 }
• On the control of resonant versus non-resonant electronic transitions in molecular photodissociation. Gräfe, Stefanie; Engel, Volker. In Chemical Physics Letters, 414(1), S. 17–22. 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{GRAFE200517, author = {Gräfe, Stefanie and Engel, Volker}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 1, pages = {17 - 22}, title = {On the control of resonant versus non-resonant electronic transitions in molecular photodissociation}, volume = 414, year = 2005 }
• Vibronic energies and spectra of molecular dimers. Eisfeld, A.; Braun, L.; Strunz, W. T.; Briggs, J. S.; Beck, J.; Engel, V. In The Journal of Chemical Physics, 122(13), S. 134103. {AIP} Publishing, 2005.
  • [ BibTeX ]
  • [ DOI ]
  @article{Eisfeld_2005, author = {Eisfeld, A. and Braun, L. and Strunz, W. T. and Briggs, J. S. and Beck, J. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {04}, number = 13, pages = 134103, publisher = {{AIP} Publishing}, title = {Vibronic energies and spectra of molecular dimers}, volume = 122, year = 2005 }

• Time-dependent electron localization functions for coupled nuclear-electronic motion. Erdmann, M.; Gross, E. K. U.; Engel, V. In The Journal of Chemical Physics, 121(19), S. 9666–9670. {AIP} Publishing, 2004.
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  • [ DOI ]
  @article{Erdmann_2004, author = {Erdmann, M. and Gross, E. K. U. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = 11, number = 19, pages = {9666–9670}, publisher = {{AIP} Publishing}, title = {Time-dependent electron localization functions for coupled nuclear-electronic motion}, volume = 121, year = 2004 }
• Combined electronic and nuclear dynamics in a simple model system. {II}. Spectroscopic transitions. Erdmann, M.; Engel, V. In The Journal of Chemical Physics, 120(1), S. 158–164. {AIP} Publishing, 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{Erdmann_2004, author = {Erdmann, M. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {01}, number = 1, pages = {158–164}, publisher = {{AIP} Publishing}, title = {Combined electronic and nuclear dynamics in a simple model system. {II}. Spectroscopic transitions}, volume = 120, year = 2004 }
• Approaches to Wave Packet Imaging Using Femtosecond Ionization Spectroscopy. Gräfe, S.; Scheidel, D.; Engel, V.; Henriksen, N. E.; Møller, K. B. In The Journal of Physical Chemistry A, 108(41), S. 8954–8960. 2004.
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  • [ DOI ]
  @article{doi:10.1021/jp040230q, abstract = {Different methods to obtain information about the probability densities of vibrational wave packets in diatomic molecule are compared. More explicitly, we consider pump−probe ionization processes. Time-resolved photoelectron spectra and total ion yields as well as fragment ion distributions are calculated, and these different quantities are employed to reconstruct radial densities. It is shown that pump−probe ionization experiments are well suited for the mapping of vibrational wave packets.}, author = {Gräfe, S. and Scheidel, D. and Engel, V. and Henriksen, N. E. and Møller, K. B.}, journal = {The Journal of Physical Chemistry A}, keywords = {ak-engel}, number = 41, pages = {8954-8960}, title = {Approaches to Wave Packet Imaging Using Femtosecond Ionization Spectroscopy}, volume = 108, year = 2004 }
• Infrared spectrum and predissociation dynamics of H₂O⁺-Ar. Dopfer, O.; Engel, V. In The Journal of Chemical Physics, 121(24), S. 12345. {AIP} Publishing, 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{Dopfer_2004, author = {Dopfer, O. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, number = 24, pages = 12345, publisher = {{AIP} Publishing}, title = {Infrared spectrum and predissociation dynamics of H₂O⁺-Ar}, volume = 121, year = 2004 }
• Electronic predissociation: a model study. Erdmann, M.; Baumann, S.; Gr{ä}fe, S.; Engel, V. In The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics, 30(3), S. 327–333. 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{Erdmann2004, abstract = {The combined electronic and nuclear motion during a predissociation process is studied in a model system. The latter consists of an electron and an ion which are allowed to move in one dimension and interact with each other and two fixed ions via screened Coulomb interactions. The fragmentation dynamics is illustrated in terms of the temporal changes of electronic and nuclear densities. In this way it is possible to reveal the influence of non-adiabatic coupling, not only on the nuclear wave-packet motion, but also on the transient electronic structure.}, author = {Erdmann, M. and Baumann, S. and Gr{\"a}fe, S. and Engel, V.}, journal = {The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics}, keywords = {ak-engel}, number = 3, pages = {327–333}, title = {Electronic predissociation: a model study}, volume = 30, year = 2004 }
• Fractional revivals in the rovibrational motion of I₂. Lohmüller, T.; Engel, V.; Beswick, J. A.; Meier, C. In The Journal of Chemical Physics, 120(22), S. 10442–10449. {AIP} Publishing, 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{Lohm_ller_2004, author = {Lohmüller, T. and Engel, V. and Beswick, J. A. and Meier, C.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {06}, number = 22, pages = {10442–10449}, publisher = {{AIP} Publishing}, title = {Fractional revivals in the rovibrational motion of I₂}, volume = 120, year = 2004 }
• Molecular orientation via a dynamically induced pulse-train: Wave packet dynamics of {NaI} in a static electric field. Marquetand, P.; Materny, A.; Henriksen, N. E.; Engel, V. In The Journal of Chemical Physics, 120(13), S. 5871–5874. {AIP} Publishing, 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{Marquetand_2004, author = {Marquetand, P. and Materny, A. and Henriksen, N. E. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {04}, number = 13, pages = {5871–5874}, publisher = {{AIP} Publishing}, title = {Molecular orientation via a dynamically induced pulse-train: Wave packet dynamics of {NaI} in a static electric field}, volume = 120, year = 2004 }
• How Delocalized Is N,N,N‘,N‘-Tetraphenylphenylenediamine Radical Cation? An Experimental and Theoretical Study on the Electronic and Molecular Structure. Szeghalmi, Adriana V.; Erdmann, Marco; Engel, Volker; Schmitt, Michael; Amthor, Stephan; Kriegisch, Volker; Nöll, Gilbert; Stahl, Rainer; Lambert, Christoph; Leusser, Dirk; Stalke, Dietmar; Zabel, Manfred; Popp, Jürgen. In Journal of the American Chemical Society, 126(25), S. 7834–7845. 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/ja0395386, abstract = {The electronic and molecular structure of N,N,N‘,N‘-tetraphenylphenylenediamine radical cation 1+ is in focus of this study. Resonance Raman experiments showed that at least eight vibrational modes are strongly coupled to the optical charge resonance band which is seen in the NIR. With the help of a DFT-based vibrational analysis, these eight modes were assigned to symmetric vibrations. The contribution of these symmetric modes to the total vibrational reorganization energy is dominant. These findings are in agreement with the conclusions from a simple two-state two-mode Marcus−Hush analysis which yields a tiny electron-transfer barrier. The excellent agreement of the X-ray crystal structure analysis and the DFT computed molecular structure of 1+ on one hand as well as the solvent and solid-state IR spectra and the DFT-calculated IR active vibrations on the other hand prove 1+ adopts a symmetrical delocalized Robin−Day class III structure both in the solid state and in solution.}, author = {Szeghalmi, Adriana V. and Erdmann, Marco and Engel, Volker and Schmitt, Michael and Amthor, Stephan and Kriegisch, Volker and Nöll, Gilbert and Stahl, Rainer and Lambert, Christoph and Leusser, Dirk and Stalke, Dietmar and Zabel, Manfred and Popp, Jürgen}, journal = {Journal of the American Chemical Society}, keywords = {ak-engel}, note = {PMID: 15212531}, number = 25, pages = {7834-7845}, title = {How Delocalized Is N,N,N‘,N‘-Tetraphenylphenylenediamine Radical Cation? An Experimental and Theoretical Study on the Electronic and Molecular Structure}, volume = 126, year = 2004 }
• Indirect versus direct photoionization with ultrashort pulses: interferences and time-resolved bond-length changes. Gräfe, S.; Engel, V. In Chemical Physics Letters, 385(1), S. 60–65. 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{GRAFE200460, author = {Gräfe, S. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 1, pages = {60 - 65}, title = {Indirect versus direct photoionization with ultrashort pulses: interferences and time-resolved bond-length changes}, volume = 385, year = 2004 }
• Quantum control fields from instantaneous dynamics. Gräfe, Stefanie; Marquetand, Philipp; Engel, Volker; Henriksen, Niels E.; Møller, Klaus B. In Chemical Physics Letters, 398(1), S. 180–185. 2004.
  • [ BibTeX ]
  • [ DOI ]
  @article{GRAFE2004180, author = {Gräfe, Stefanie and Marquetand, Philipp and Engel, Volker and Henriksen, Niels E. and Møller, Klaus B.}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 1, pages = {180 - 185}, title = {Quantum control fields from instantaneous dynamics}, volume = 398, year = 2004 }

• Probing the Kinetics of a Nonadiabatic Transition Initiating Out of Vibrationally Excited as Well as Ground State Modes with Femtosecond Time-Resolved Transient Gratings. Siebert, T.; Engel, V.; Materny, A.; Kiefer, W.; Schmitt, M. In The Journal of Physical Chemistry A, 107(40), S. 8355–8362. 2003.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jp022650q, abstract = {Femtosecond time-resolved population gratings are employed for observing the kinetics of vibrational cooling and internal conversion in the S1 state of β-carotene. Two independent laser pulses, which are tuned resonant to the S2 ← S0 optical transition induce transient population gratings into solutions of β-carotene. Because the S2 state lies approximately 6000 cm-1 above the S1 potential, the subsequent internal conversion to the S1 state generates a population grating of hot vibrational modes on the S1 potential. This is followed by vibrational cooling and an internal conversion to the electronic ground state. The kinetics associated with these processes are interrogated by scattering a third, time-variable probe pulse off the S1 state population gratings under Bragg conditions. When the probe laser pulse is tuned to different wavelengths within the red flank of the Sn ← S1 absorption profile, excited vibrational states as well as the vibrational ground state modes in the S1 potential can selectively be monitored. This is verified by characterizing the contribution of vibrational cooling to the acquired kinetics. With a comparison between the kinetics observed for excited and ground state vibrational modes, it can be shown that the rate of the S1/S0 internal conversion increases for hot vibrational modes.}, author = {Siebert, T. and Engel, V. and Materny, A. and Kiefer, W. and Schmitt, M.}, journal = {The Journal of Physical Chemistry A}, keywords = {AK-Engel}, number = 40, pages = {8355-8362}, title = {Probing the Kinetics of a Nonadiabatic Transition Initiating Out of Vibrationally Excited as Well as Ground State Modes with Femtosecond Time-Resolved Transient Gratings}, volume = 107, year = 2003 }
• The mechanism of light storage in spherical microcavities explored on a femtosecond time scale. Siebert, T.; Sbanski, O.; Schmitt, M.; Engel, V.; Kiefer, W.; Popp, J. In Optics Communications, 216(4), S. 321–327. 2003.
  • [ BibTeX ]
  • [ DOI ]
  @article{SIEBERT2003321, author = {Siebert, T. and Sbanski, O. and Schmitt, M. and Engel, V. and Kiefer, W. and Popp, J.}, journal = {Optics Communications}, keywords = {ak-engel}, number = 4, pages = {321 - 327}, title = {The mechanism of light storage in spherical microcavities explored on a femtosecond time scale}, volume = 216, year = 2003 }
• Photodissociation and recombination dynamics of I₂ in DDR (decadodecasil 3R): Dependence on the geometry of the host matrix monitored by femtosecond time-resolved pump-probe experiments. Flachenecker, G.; Ermoshin, V. A.; Engel, V.; Neder, R.; Wirnsberger, G.; Materny, A. In Phys. Chem. Chem. Phys., 5(5), S. 865–876. The Royal Society of Chemistry, 2003.
  • [ BibTeX ]
  • [ DOI ]
  @article{B210290K, abstract = {We present polarization dependent femtosecond time-resolved pump-probe experiments on iodine molecules embedded in well-defined cages of the crystalline microporous SiO2 modification decadodecasil 3R (DDR). Inside the DDR porosils the I2 molecules reside isolated from each other in hexagonal cages of [approximate]350 A3. After pump excitation of the B 0+u (3[capital Pi]) state{,} the collision induced dissociation takes place via different crossing repulsive potential curves. The surrounding cages cause the atoms to recombine. The resulting iodine molecules are prepared in their A{,} A[prime or minute]{,} and X states where vibrational relaxation takes place due to the collisions with the surroundings. For a better understanding of the complex dynamics{,} a theoretical model was developed based on the classical Langevin equation (Brownian dynamics). The simulations of the experimental data obtained from powder samples are compared with earlier calculations by Ermoshin et al. (V. A. Ermoshin{,} G. Flachenecker{,} A. Materny and V. Engel{,} J. Chem. Phys.{,} 2001{,} 114{,} 8132) based on molecular dynamics modeling. Brownian dynamics simulations are also applied to polarization dependent pump-probe experiments on single crystalline I2-DDR samples. It is demonstrated{,} that by switching the polarization of the lasers relative to the crystal axis the predissociation process of the excited B state of I2 can be influenced. This effect can be simulated using the theoretical model.}, author = {Flachenecker, G. and Ermoshin, V. A. and Engel, V. and Neder, R. and Wirnsberger, G. and Materny, A.}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 5, pages = {865-876}, publisher = {The Royal Society of Chemistry}, title = {Photodissociation and recombination dynamics of I₂ in DDR (decadodecasil 3R): Dependence on the geometry of the host matrix monitored by femtosecond time-resolved pump-probe experiments}, volume = 5, year = 2003 }
• Combined electronic and nuclear dynamics in a simple model system. Erdmann, M.; Marquetand, P.; Engel, V. In The Journal of Chemical Physics, 119(2), S. 672–679. {AIP} Publishing, 2003.
  • [ BibTeX ]
  • [ DOI ]
  @article{Erdmann_2003, author = {Erdmann, M. and Marquetand, P. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = {07}, number = 2, pages = {672–679}, publisher = {{AIP} Publishing}, title = {Combined electronic and nuclear dynamics in a simple model system}, volume = 119, year = 2003 }
• Chirped pulse ionization: bondlength dynamics and interference effects. Lohmüller, T.; Erdmann, M.; Engel, V. In Chemical Physics Letters, 373(3), S. 319–327. 2003.
  • [ BibTeX ]
  • [ DOI ]
  @article{LOHMULLER2003319, author = {Lohmüller, T. and Erdmann, M. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 3, pages = {319 - 327}, title = {Chirped pulse ionization: bondlength dynamics and interference effects}, volume = 373, year = 2003 }
• Determination of transition dipole moments from time–resolved photoelectron spectroscopy. {Lohmüller, T.}; {Erdmann, M.}; {Rubner, O.}; {Engel, V.}. In Eur. Phys. J. D, 25(1), S. 95–99. 2003.
  • [ BibTeX ]
  • [ DOI ]
  @article{refId0, author = {{Lohmüller, T.} and {Erdmann, M.} and {Rubner, O.} and {Engel, V.}}, journal = {Eur. Phys. J. D}, keywords = {ak-engel}, number = 1, pages = {95-99}, title = {Determination of transition dipole moments from time–resolved photoelectron spectroscopy}, volume = 25, year = 2003 }

• Fermi–Pasta–Ulam recurrences, normal modes and wave-packet revivals. Ermoshin, V.A.; Erdmann, M.; Engel, V. In Chemical Physics Letters, 356(1), S. 29–35. 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{ERMOSHIN200229, author = {Ermoshin, V.A. and Erdmann, M. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 1, pages = {29 - 35}, title = {Fermi–Pasta–Ulam recurrences, normal modes and wave-packet revivals}, volume = 356, year = 2002 }
• Cationic molecular wave packets: "Settin’ the pace". Gräfe S.; Erdmann, M.; Engel, V. In The Journal of Chemical Physics, 116(12), S. 4762. {AIP} Publishing, 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{Gra_fe_2002, author = {Gräfe, S. and Erdmann, M. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, number = 12, pages = 4762, publisher = {{AIP} Publishing}, title = {Cationic molecular wave packets: "Settin' the pace"}, volume = 116, year = 2002 }
• Target wave-packet control and its detection using time-resolved photoelectron spectroscopy. Shen, Z.; Engel, V. In Chemical Physics Letters, 358(3), S. 344–349. 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{SHEN2002344, author = {Shen, Z. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 3, pages = {344 - 349}, title = {Target wave-packet control and its detection using time-resolved photoelectron spectroscopy}, volume = 358, year = 2002 }
• Optimal pump{\textendash}dump control and time-frequency resolved spectroscopy of ground-state wave-packet focusing. Shen, Zhenwen; Engel, Volker; Xu, Ruixue; Cheng, Jixin; Yan, YiJing. In The Journal of Chemical Physics, 117(13), S. 6142–6147. {AIP} Publishing, 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{Shen_2002, author = {Shen, Zhenwen and Engel, Volker and Xu, Ruixue and Cheng, Jixin and Yan, YiJing}, journal = {The Journal of Chemical Physics}, keywords = {ak-engel}, month = 10, number = 13, pages = {6142–6147}, publisher = {{AIP} Publishing}, title = {Optimal pump{\textendash}dump control and time-frequency resolved spectroscopy of ground-state wave-packet focusing}, volume = 117, year = 2002 }
• Strong-field ionization dynamics of a model H₂ molecule. Lein, Manfred; Kreibich, Thomas; Gross, E. K. U.; Engel, Volker. In Physical Review A, 65(3). American Physical Society ({APS}), 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{Lein2002, author = {Lein, Manfred and Kreibich, Thomas and Gross, E. K. U. and Engel, Volker}, journal = {Physical Review A}, keywords = {ak-engel}, month = {02}, number = 3, publisher = {American Physical Society ({APS})}, title = {Strong-field ionization dynamics of a model H₂ molecule}, volume = 65, year = 2002 }
• Applications of the Karhunen-Lo{{è}}ve Decomposition to Quantum Dynamical Problems. Dietz, H.; Marek, M.; M{ü}nster, A.F.; Engel, V. In Zeitschrift f{ü}r Physikalische Chemie, 216(3/2002). Walter de Gruyter {GmbH}, 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{Dietz2002, author = {Dietz, H. and Marek, M. and M\"{u}nster, A.F. and Engel, V.}, journal = {Zeitschrift f\"{u}r Physikalische Chemie}, keywords = {ak-engel}, month = {01}, number = {3/2002}, publisher = {Walter de Gruyter {GmbH}}, title = {Applications of the Karhunen-Lo{\`{e}}ve Decomposition to Quantum Dynamical Problems}, volume = 216, year = 2002 }
• Femtosecond time-resolved photoelectron spectroscopy with high frequency probe pulses. Erdmann, M; Shen, Z; Engel, V. In Chemical Physics Letters, 351(3), S. 275–280. 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{ERDMANN2002275, author = {Erdmann, M and Shen, Z and Engel, V}, journal = {Chemical Physics Letters}, keywords = {ak-engel}, number = 3, pages = {275 - 280}, title = {Femtosecond time-resolved photoelectron spectroscopy with high frequency probe pulses}, volume = 351, year = 2002 }
• Population Dynamics in Vibrational Modes during Non-Born−Oppenheimer Processes:  CARS Spectroscopy Used as a Mode-Selective Filter. Siebert, Torsten; Schmitt, Michael; Engel, Volker; Materny, Arnulf; Kiefer, Wolfgang. In Journal of the American Chemical Society, 124(22), S. 6242–6243. 2002.
  • [ BibTeX ]
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  @article{doi:10.1021/ja0173831, abstract = {The coupling of specific nuclear and electronic degrees of freedom of a molecular system during non-radiative electronic transitions plays a central role in photochemistry and photobiology. This breakdown of the Born-Oppenheimer approximation during processes such as internal conversion determines the mechanism and product distribution of photochemical reactions and is responsible for the high efficiency of photobiological processes. In order to explore this phenomena in β-carotene, a molecule that plays a primary role as an auxiliary light-harvesting pigment in photosynthesis, a spectroscopic method was employed that allows for the individual vibrational modes to be monitored selectively within the dynamics of an internal conversion process. This spectroscopic technique employs an initial pump laser to excite the molecule into an excited electronic state and resolves the subsequent relaxation process by interrogating the system with a time-delayed, coherent anti-Stokes Raman process (CARS), which acts as a mode-selective filter for observing the population flow within specific vibrational modes with a time resolution in the femtosecond regime.}, author = {Siebert, Torsten and Schmitt, Michael and Engel, Volker and Materny, Arnulf and Kiefer, Wolfgang}, journal = {Journal of the American Chemical Society}, keywords = {ak-engel}, note = {PMID: 12033844}, number = 22, pages = {6242-6243}, title = {Population Dynamics in Vibrational Modes during Non-Born−Oppenheimer Processes:  CARS Spectroscopy Used as a Mode-Selective Filter}, volume = 124, year = 2002 }
• Time-resolved photoelectron spectroscopy:. Erdmann, M; Rubner, O; Shen, Z; Engel, V. In Journal of Organometallic Chemistry, 661(1), S. 191–197. 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{ERDMANN2002191, author = {Erdmann, M and Rubner, O and Shen, Z and Engel, V}, journal = {Journal of Organometallic Chemistry}, keywords = {ak-engel}, number = 1, pages = {191 - 197}, title = {Time-resolved photoelectron spectroscopy:}, volume = 661, year = 2002 }
• Time-resolved photoelectron spectroscopy of molecular dissociation: Classical trajectory versus quantum wave-packet calculations. Meier, Christoph; Engel, Volker. In Phys. Chem. Chem. Phys., 4(20), S. 5014–5019. The Royal Society of Chemistry, 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{B205417E, abstract = {We present a simulation of ultrafast pump-probe photoelectron spectroscopy based on a classical treatment of the nuclear motion. A comparison with quantum mechanical wave-packet results shows that in the case of the direct dissociation of H2O in its A 1B1 electronic state this method produces extremely accurate results. The energy distribution of the photoelectrons recorded as a function of the pump-probe delay reflects the dissociation process{,} which takes place within only a few femtoseconds.}, author = {Meier, Christoph and Engel, Volker}, journal = {Phys. Chem. Chem. Phys.}, keywords = {ak-engel}, number = 20, pages = {5014-5019}, publisher = {The Royal Society of Chemistry}, title = {Time-resolved photoelectron spectroscopy of molecular dissociation: Classical trajectory versus quantum wave-packet calculations}, volume = 4, year = 2002 }
• The Effect of the Electron-Electron Interaction in Above-Threshold Double Ionization. Lein, Manfred; Gross, E.K.U.; Engel, Volker. In Laser Physics, 12(2), S. 487–490. 2002.
  • [ BibTeX ]
  @article{noauthororeditor, author = {Lein, Manfred and Gross, E.K.U. and Engel, Volker}, journal = {Laser Physics}, keywords = {ak-engel}, number = 2, pages = {487-490}, title = {The Effect of the Electron-Electron Interaction in Above-Threshold Double Ionization}, volume = 12, year = 2002 }
• The role of specific normal modes during non-Born–Oppenheimer dynamics: the S1–S0 internal conversion of β-carotene interrogated on a femtosecond time-scale with coherent anti-Stokes Raman scattering. Siebert, T.; Maksimenka, R.; Materny, A.; Engel, V.; Kiefer, W.; Schmitt, M. In Journal of Raman Spectroscopy, 33(11-12), S. 844–854. John Wiley & Sons, Ltd., 2002.
  • [ BibTeX ]
  • [ DOI ]
  @article{JRS:JRS926, abstract = {The population flow from the first excited singlet state (S1) to the electronic ground state (S0), facilitated through the S1–S0 internal conversion, and the subsequent internal vibrational energy redistribution and vibrational cooling processes are monitored selectively with respect to the different forms of nuclear motion in all-trans-β-carotene. This is realized by exciting the molecule into the second excited singlet state (S2) with an auxiliary pump laser pulse and interrogating the population recovery into the electronic ground state by means of a time-delayed, coherent anti-Stokes Raman (CARS) process. This spectroscopic scheme is referred to as a pump-CARS scheme in analogy to the classical pump–probe scheme in time-resolved spectroscopy. Here, the profound enhancement of the CARS signal intensity in the case of a Raman resonance to a specific vibrational mode is utilized as an intensity filter that amplifies the signal from the vibrational modes of interest, making the contributions from other vibrational modes negligible. This filter allows for the population flow in a specific vibrational mode to be monitored as the radiationless electronic transition between the S1 and S0 state takes place. This spectroscopic scheme opens up the possibility of identifying the vibrational motion with a large-amplitude motion in the CC double bond symmetric stretch as the primary acceptor of population from the S1 state. A mechanism with which the other normal modes are populated is postulated. Copyright © 2002 John Wiley & Sons, Ltd.}, author = {Siebert, T. and Maksimenka, R. and Materny, A. and Engel, V. and Kiefer, W. and Schmitt, M.}, journal = {Journal of Raman Spectroscopy}, keywords = {ak-engel}, number = {11-12}, pages = {844–854}, publisher = {John Wiley & Sons, Ltd.}, title = {The role of specific normal modes during non-Born–Oppenheimer dynamics: the S1–S0 internal conversion of β-carotene interrogated on a femtosecond time-scale with coherent anti-Stokes Raman scattering}, volume = 33, year = 2002 }

• Phase-energy approach to collision-induced vibrational relaxation. Kazansky, A. K.; Ermoshin, V. A.; Engel, V. In The Journal of Chemical Physics, 113(20), S. 8865–8868. {AIP} Publishing, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{Kazansky_2000, author = {Kazansky, A. K. and Ermoshin, V. A. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = 11, number = 20, pages = {8865–8868}, publisher = {{AIP} Publishing}, title = {Phase-energy approach to collision-induced vibrational relaxation}, volume = 113, year = 2000 }
• Oscillatory pump{\textendash}probe signals from delocalized wave packets. Ermoshin, V. A.; Engel, V.; Meier, C. In The Journal of Chemical Physics, 113(14), S. 5770–5775. {AIP} Publishing, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{Ermoshin_2000, author = {Ermoshin, V. A. and Engel, V. and Meier, C.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = 10, number = 14, pages = {5770–5775}, publisher = {{AIP} Publishing}, title = {Oscillatory pump{\textendash}probe signals from delocalized wave packets}, volume = 113, year = 2000 }
• Collision-induced bound state motion in I₂. A classical molecular dynamics study. Ermoshin, V. A.; Engel, V.; Meier, C. In The Journal of Chemical Physics, 113(16), S. 6585–6591. {AIP} Publishing, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{Ermoshin_2000, author = {Ermoshin, V. A. and Engel, V. and Meier, C.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = 10, number = 16, pages = {6585–6591}, publisher = {{AIP} Publishing}, title = {Collision-induced bound state motion in I₂. A classical molecular dynamics study}, volume = 113, year = 2000 }
• Mapping of wave packets in direct fragmentation via pump{\textendash}probe frequency integrated fluorescence spectroscopy. Engel, V.; Henriksen, N. E. In The Journal of Chemical Physics, 112(1), S. 106–111. {AIP} Publishing, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{Engel_2000, author = {Engel, V. and Henriksen, N. E.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {01}, number = 1, pages = {106–111}, publisher = {{AIP} Publishing}, title = {Mapping of wave packets in direct fragmentation via pump{\textendash}probe frequency integrated fluorescence spectroscopy}, volume = 112, year = 2000 }
• Stochastic trajectory simulation of femtosecond pump{\textendash}probe spectroscopy. Ermoshin, V.A.; Engel, V. In Chemical Physics Letters, 332(1-2), S. 110–116. Elsevier {BV}, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{Ermoshin2000, author = {Ermoshin, V.A. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = 12, number = {1-2}, pages = {110–116}, publisher = {Elsevier {BV}}, title = {Stochastic trajectory simulation of femtosecond pump{\textendash}probe spectroscopy}, volume = 332, year = 2000 }
• Molecular Dynamics Simulation of Femtosecond Pump-Probe Experiments on I₂ in Ar Environments. Ermoshin, V.A.; Engel, V. In Zeitschrift f{ü}r Physikalische Chemie, 214(9). Walter de Gruyter {GmbH}, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{Ermoshin2000, author = {Ermoshin, V.A. and Engel, V.}, journal = {Zeitschrift f\"{u}r Physikalische Chemie}, keywords = {myown}, month = {01}, number = 9, publisher = {Walter de Gruyter {GmbH}}, title = {Molecular Dynamics Simulation of Femtosecond Pump-Probe Experiments on I₂ in Ar Environments}, volume = 214, year = 2000 }
• Intense-Field Double Ionization of Helium: Identifying the Mechanism. Lein, M.; Gross, E. K. U.; Engel, V. In Phys. Rev. Lett., 85(22), S. 4707–4710. American Physical Society, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{PhysRevLett.85.4707, author = {Lein, M. and Gross, E. K. U. and Engel, V.}, journal = {Phys. Rev. Lett.}, keywords = {myown}, month = 11, number = 22, pages = {4707–4710}, publisher = {American Physical Society}, title = {Intense-Field Double Ionization of Helium: Identifying the Mechanism}, volume = 85, year = 2000 }
• On the mechanism of strong-field double photoionization in the helium atom. Lein, M; Gross, E K U; Engel, V. In Journal of Physics B: Atomic, Molecular and Optical Physics, 33(3), S. 433. 2000.
  • [ BibTeX ]
  @article{0953-4075-33-3-312, abstract = {We perform time-dependent quantum calculations on the ionization dynamics of helium in intense ultrashort laser fields. A linear model of the atom is used to extract single- and double-ionization yields for a 780 nm excitation. For an intensity of 10 15 W cm -2 clear evidence is found for a direct double-ionization process which is caused by rescattering of an electron from the core in the presence of the field. A momentum-space analysis of the wavefunctions shows that in this case both electrons are preferentially emitted in the same direction and with different momenta.}, author = {Lein, M and Gross, E K U and Engel, V}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, keywords = {myown}, number = 3, pages = 433, title = {On the mechanism of strong-field double photoionization in the helium atom}, volume = 33, year = 2000 }
• Characterization of nuclear wave packets describing molecular photodissociation. Lein, M.; Erdmann, M.; Engel, V. In The Journal of Chemical Physics, 113(9), S. 3609–3614. {AIP} Publishing, 2000.
  • [ BibTeX ]
  • [ DOI ]
  @article{Lein_2000, author = {Lein, M. and Erdmann, M. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {09}, number = 9, pages = {3609–3614}, publisher = {{AIP} Publishing}, title = {Characterization of nuclear wave packets describing molecular photodissociation}, volume = 113, year = 2000 }
• Wave packet dynamics in different electronic states investigated by femtosecond time-resolved four-wave-mixing spectroscopy. Materny, A.; Chen, T.; Schmitt, M.; Siebert, T.; Vierheilig, A.; Engel, V.; Kiefer, W. In Applied Physics B, 71(3), S. 299–317. 2000.
  • [ BibTeX ]
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  @article{Materny2000, abstract = {This paper reviews results on wave packet dynamics investigated by means of femtosecond time-resolved four-wave-mixing (FWM) spectroscopy. First, it is shown that by making use of the various degrees of freedom which are offered by this technique information about molecular dynamics on different potential-energy surfaces can be accessed and separated from each other. By varying the timing, polarization, and wavelengths of the laser pulses as well as the wavelength of the detection window for the FWM signal, different dynamics are coherently excited and probed by the nonlinear spectroscopy. As a model system we use iodine in the gas phase. These techniques are then applied to more-complex molecules (gas phase: benzene, toluene, a binary mixture of benzene and toluene; solid state: polymers of diacetylene matrix-isolated in single crystals of monomer molecules). Here, ground-state dynamics are investigated first without any involvement of electronically excited states and then in electronic resonance to an absorption transition in the investigated molecules. Signal modulations result which are due to wave packet motion as well as polarization beats between modes in different molecules. Phase and intensity changes yield information about intramolecular vibrational energy redistribution, population decay (T1), phase relaxation (T2), and coherence times.}, author = {Materny, A. and Chen, T. and Schmitt, M. and Siebert, T. and Vierheilig, A. and Engel, V. and Kiefer, W.}, journal = {Applied Physics B}, keywords = {myown}, month = {09}, number = 3, pages = {299–317}, title = {Wave packet dynamics in different electronic states investigated by femtosecond time-resolved four-wave-mixing spectroscopy}, volume = 71, year = 2000 }
• Pulse-width and isotope effects in femtosecond-pulse strong-field dissociation of H₂⁺ and D₂⁺. Trump, C.; Rottke, H.; Wittmann, M.; Korn, G.; Sandner, W.; Lein, M.; Engel, V. In Phys. Rev. A, 62(6), S. 063402. American Physical Society, 2000.
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  @article{PhysRevA.62.063402, author = {Trump, C. and Rottke, H. and Wittmann, M. and Korn, G. and Sandner, W. and Lein, M. and Engel, V.}, journal = {Phys. Rev. A}, keywords = {myown}, month = 10, number = 6, pages = {063402}, publisher = {American Physical Society}, title = {Pulse-width and isotope effects in femtosecond-pulse strong-field dissociation of H₂⁺ and D₂⁺}, volume = 62, year = 2000 }
• Hybrid quantum/classical study of {ICN} in an Ar matrix: Photofragmentation and cage exit. Alberti, S. Fernandez; Echave, J.; Engel, V.; Halberstadt, N.; Beswick, J. A. In The Journal of Chemical Physics, 113(3), S. 1027–1034. {AIP} Publishing, 2000.
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  @article{Fernandez_Alberti_2000, author = {Alberti, S. Fernandez and Echave, J. and Engel, V. and Halberstadt, N. and Beswick, J. A.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {07}, number = 3, pages = {1027–1034}, publisher = {{AIP} Publishing}, title = {Hybrid quantum/classical study of {ICN} in an Ar matrix: Photofragmentation and cage exit}, volume = 113, year = 2000 }
• Non-perturbative wave-packet calculations of time-resolved four-wave-mixing signals. Meyer, S.; Engel, V. In Applied Physics B, 71(3), S. 293–297. 2000.
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  @article{Meyer2000, abstract = {We extend a method proposed by Seidner et al. [J. Chem. Phys. 103, 3998 (1995)] to extract directional terms from a time-dependent molecular polarization to obtain time-resolved four-wave-mixing (FWM) signals. Instead of employing perturbation theory, the total polarization induced in the molecular sample by the interaction with several femtosecond laser pulses is determined by solving the time-dependent Schr{\"o}dinger equation for the nuclear dynamics in coupled electronic states numerically exact. Repeating the calculation for several combinations of relative phases of the involved fields leads to a linear system of equations for the contributions emitted in different directions. Gas-phase I2 molecules serve as a numerical example.}, author = {Meyer, S. and Engel, V.}, journal = {Applied Physics B}, keywords = {myown}, month = {09}, number = 3, pages = {293–297}, title = {Non-perturbative wave-packet calculations of time-resolved four-wave-mixing signals}, volume = 71, year = 2000 }
• Femtosecond time-resolved CARS and DFWM spectroscopy on gas-phase I₂: a wave-packet description. Meyer, S.; Engel, V. In Journal of Raman Spectroscopy, 31(1-2), S. 33–39. John Wiley & Sons, Ltd., 2000.
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  @article{JRS:JRS494, abstract = {Femtosecond time-resolved CARS (coherent anti-Stokes Raman scattering) and DFWM (degenerate four-wave mixing) experiments on gas-phase iodine molecules were analyzed within time dependent wave-packet calculations. The recorded signals were interpreted using the ro-vibrational quantum dynamics in different electronic states of I2. Thereby various contributions to the induced third-order polarization were related to overlap integrals between wave packets created by absorption and emission processes. This allows for an intuitive interpretation of the temporal variations in the signals. Copyright © 2000 John Wiley & Sons, Ltd.}, author = {Meyer, S. and Engel, V.}, journal = {Journal of Raman Spectroscopy}, keywords = {myown}, number = {1-2}, pages = {33–39}, publisher = {John Wiley & Sons, Ltd.}, title = {Femtosecond time-resolved CARS and DFWM spectroscopy on gas-phase I₂: a wave-packet description}, volume = 31, year = 2000 }
• Separation of vibrational and rotational coherences with polarized femtosecond time-resolved four-wave mixing spectroscopy. Siebert, T.; Schmitt, M.; Vierheilig, A.; Flachenecker, G.; Engel, V.; Materny, A.; Kiefer, W. In Journal of Raman Spectroscopy, 31(1-2), S. 25–31. John Wiley & Sons, Ltd., 2000.
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  @article{JRS:JRS521, abstract = {One of the degrees of freedom available to femtosecond time-resolved four-wave mixing spectroscopy is the geometry with which the polarization of the three independent lasers employed in this technique are oriented relative to one another. In the work presented here, different polarization geometries were used to demonstrate the selectivity that can be achieved with respect to the rotational and vibrational dynamics observed in a femtosecond time-resolved four-wave mixing transient. Two of the polarization geometries presented here allow for the simultaneous observation of rotational and vibrational coherences and furthermore illustrate the mechanism with which the rotational dynamics enter into the signal. A third ‘magic angle’ polarization geometry allows for the complete elimination of the rotational coherences from the signal, which makes full characterization of the vibrational dynamics in the four-wave mixing signal possible. This is shown for the dynamics in both an electronically excited and the electronic ground state of gaseous iodine, which serves as a model system. The results are discussed in a wave-packet picture which applies under the present experimental conditions where any damping mechanism can safely be neglected. Copyright © 2000 John Wiley & Sons, Ltd.}, author = {Siebert, T. and Schmitt, M. and Vierheilig, A. and Flachenecker, G. and Engel, V. and Materny, A. and Kiefer, W.}, journal = {Journal of Raman Spectroscopy}, keywords = {myown}, number = {1-2}, pages = {25–31}, publisher = {John Wiley & Sons, Ltd.}, title = {Separation of vibrational and rotational coherences with polarized femtosecond time-resolved four-wave mixing spectroscopy}, volume = 31, year = 2000 }
• Theoretical analysis of femtosecond excitation and fragmentation dynamics of Fe({CO})₅. Rubner, O.; Baumert, T.; Bergt, M.; Kiefer, B.; Gerber, G.; Engel, V. In Chemical Physics Letters, 316(5-6), S. 585–592. Elsevier {BV}, 2000.
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  @article{Rubner2000, author = {Rubner, O. and Baumert, T. and Bergt, M. and Kiefer, B. and Gerber, G. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {01}, number = {5-6}, pages = {585–592}, publisher = {Elsevier {BV}}, title = {Theoretical analysis of femtosecond excitation and fragmentation dynamics of Fe({CO})₅}, volume = 316, year = 2000 }

• Ultrafast detection and control of molecular dynamics. Anfinrud, P.; de Vivie-Riedle, R.; Engel, V. In Proceedings of the National Academy of Sciences, 96(15), S. 8328–8329. Proceedings of the National Academy of Sciences, 1999.
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  @article{Anfinrud1999, author = {Anfinrud, P. and de Vivie-Riedle, R. and Engel, V.}, journal = {Proceedings of the National Academy of Sciences}, keywords = {myown}, month = {07}, number = 15, pages = {8328–8329}, publisher = {Proceedings of the National Academy of Sciences}, title = {Ultrafast detection and control of molecular dynamics}, volume = 96, year = 1999 }
• Classical simulations on the pump–probe spectroscopy of I₂ encapsulated in DDR porosil. Ermoshin, V A.; Flachenecker, G; Materny, A; Engel, V. In Chemical Physics Letters, 311(3-4), S. 146–152. Elsevier {BV}, 1999.
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  @article{AErmoshin1999, author = {Ermoshin, V A. and Flachenecker, G and Materny, A and Engel, V}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {09}, number = {3-4}, pages = {146–152}, publisher = {Elsevier {BV}}, title = {Classical simulations on the pump–probe spectroscopy of I₂ encapsulated in DDR porosil}, volume = 311, year = 1999 }
• A CASSCF/MR-CCI study of the excited states of Fe(CO)₅. Rubner, O; Engel, V; Hachey, M.R; Daniel, C. In Chemical Physics Letters, 302(5-6), S. 489–494. Elsevier {BV}, 1999.
  • [ BibTeX ]
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  @article{Rubner1999, author = {Rubner, O and Engel, V and Hachey, M.R and Daniel, C}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {03}, number = {5-6}, pages = {489–494}, publisher = {Elsevier {BV}}, title = {A CASSCF/MR-CCI study of the excited states of Fe(CO)₅}, volume = 302, year = 1999 }
• Quantum-classical molecular dynamics simulation of femtosecond spectroscopy on I₂ in inert gases: Mechanisms for the decay of pump{\textendash}probe signals. Ermoshin, V. A.; Kazansky, A. K.; Engel, V. In The Journal of Chemical Physics, 111(17), S. 7807–7817. {AIP} Publishing, 1999.
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  @article{Ermoshin_1999, author = {Ermoshin, V. A. and Kazansky, A. K. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = 11, number = 17, pages = {7807–7817}, publisher = {{AIP} Publishing}, title = {Quantum-classical molecular dynamics simulation of femtosecond spectroscopy on I₂ in inert gases: Mechanisms for the decay of pump{\textendash}probe signals}, volume = 111, year = 1999 }
• A novel mixed quantum/classical method for the dynamics of molecules in a gas environment with an application to femtosecond time-resolved spectroscopy. Ermoshin, V.A.; Kazansky, A.K.; Engel, V. In Chemical Physics Letters, 302(1-2), S. 20–26. Elsevier {BV}, 1999.
  • [ BibTeX ]
  • [ DOI ]
  @article{Ermoshin1999, author = {Ermoshin, V.A. and Kazansky, A.K. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {03}, number = {1-2}, pages = {20–26}, publisher = {Elsevier {BV}}, title = {A novel mixed quantum/classical method for the dynamics of molecules in a gas environment with an application to femtosecond time-resolved spectroscopy}, volume = 302, year = 1999 }
• Determination of wave packet dynamics by femtosecond time-resolved pump-dump-probe and four-wave mixing techniques. Chen, T.; Engel, V.; Heid, M.; Kiefer, W.; Knopp, G.; Materny, A.; Meyer, S.; Pausch, R.; Schmitt, M.; Schwoerer, H.; Siebert, T. In Journal of Molecular Structure, 480-481, S. 33–43. Elsevier {BV}, 1999.
  • [ BibTeX ]
  • [ DOI ]
  @article{Chen1999, author = {Chen, T. and Engel, V. and Heid, M. and Kiefer, W. and Knopp, G. and Materny, A. and Meyer, S. and Pausch, R. and Schmitt, M. and Schwoerer, H. and Siebert, T.}, journal = {Journal of Molecular Structure}, keywords = {myown}, month = {05}, pages = {33–43}, publisher = {Elsevier {BV}}, title = {Determination of wave packet dynamics by femtosecond time-resolved pump-dump-probe and four-wave mixing techniques}, volume = {480-481}, year = 1999 }
• On the deconvolution of the temporal width of laser pulses from pump{\textendash}probe signals. Henriksen, Niels E.; Engel, Volker. In The Journal of Chemical Physics, 111(23), S. 10469–10475. {AIP} Publishing, 1999.
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  @article{Henriksen_1999, author = {Henriksen, Niels E. and Engel, Volker}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = 12, number = 23, pages = {10469–10475}, publisher = {{AIP} Publishing}, title = {On the deconvolution of the temporal width of laser pulses from pump{\textendash}probe signals}, volume = 111, year = 1999 }
• Single and multiple collision effects observed in the femtosecond spectroscopy of I₂-rare gas collision complexes: a statistical description. Dietz, H.; Engel, V. In The Journal of Chemical Physics, 110(7), S. 3335–3340. {AIP} Publishing, 1999.
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  @article{Dietz_1999, author = {Dietz, H. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {02}, number = 7, pages = {3335–3340}, publisher = {{AIP} Publishing}, title = {Single and multiple collision effects observed in the femtosecond spectroscopy of I₂-rare gas collision complexes: a statistical description}, volume = 110, year = 1999 }
• Structures in molecular photofragment and photoelectron distributions from two-photon non-resonant excitation. Herwig, A.; Braun, M.; Engel, V. In Chemical Physics Letters, 300(3-4), S. 269–274. Elsevier {BV}, 1999.
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  @article{Herwig1999, author = {Herwig, A. and Braun, M. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {02}, number = {3-4}, pages = {269–274}, publisher = {Elsevier {BV}}, title = {Structures in molecular photofragment and photoelectron distributions from two-photon non-resonant excitation}, volume = 300, year = 1999 }
• Construction of a Potential Energy Surface for Molecular Dynamics Studies of Methane Adsorbed in Zeolites. Ermoshin, V. A.; Engel, V. In The Journal of Physical Chemistry A, 103(26), S. 5116–5122. 1999.
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  @article{doi:10.1021/jp9843860, abstract = {A potential for the interaction of methane molecules with the framework atoms of siliceous zeolites is developed empirically. The CH4 molecule is considered in the spherical approximation. The interaction potential includes repulsion, dispersion, and induction energy. It is shown that even if the effective charges on the framework oxygen and silicon atoms are large, the contribution of the induction energy is weak in comparison with those of dispersion and repulsion energies due to compensation effects. The calculated parameters of a Lennard-Jones potential are compared with those used in previous MD calculations. As an application we calculate diffusion coefficients and the heat of adsorption of methane in silicalite which can be compared to available experimental data.}, author = {Ermoshin, V. A. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {myown}, number = 26, pages = {5116-5122}, title = {Construction of a Potential Energy Surface for Molecular Dynamics Studies of Methane Adsorbed in Zeolites}, volume = 103, year = 1999 }
• Simulation of femtosecond time-resolved four-wave mixing experiments on I₂. Meyer, S.; Schmitt, M.; Materny, A.; Kiefer, W.; Engel, V. In Chemical Physics Letters, 301(3-4), S. 248–254. Elsevier {BV}, 1999.
  • [ BibTeX ]
  • [ DOI ]
  @article{Meyer1999, author = {Meyer, S. and Schmitt, M. and Materny, A. and Kiefer, W. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {02}, number = {3-4}, pages = {248–254}, publisher = {Elsevier {BV}}, title = {Simulation of femtosecond time-resolved four-wave mixing experiments on I₂}, volume = 301, year = 1999 }

• Excitation of symmetric and anti-symmetric stretching motion in the continuum resonance Raman scattering from {ABA}-type molecules. Braun, M; Materny, A; Schmitt, M; Kiefer, W; Engel, V. In Chemical Physics Letters, 284(1-2), S. 39–46. Elsevier {BV}, 1998.
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  @article{Braun1998, author = {Braun, M and Materny, A and Schmitt, M and Kiefer, W and Engel, V}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {02}, number = {1-2}, pages = {39–46}, publisher = {Elsevier {BV}}, title = {Excitation of symmetric and anti-symmetric stretching motion in the continuum resonance Raman scattering from {ABA}-type molecules}, volume = 284, year = 1998 }
• An effective method for the quantum mechanical description of photoionization with ultrashort intense laser pulses. Meier, Christoph; Engel, Volker; Manthe, Uwe. In The Journal of Chemical Physics, 109(1), S. 36–41. {AIP} Publishing, 1998.
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  • [ DOI ]
  @article{Meier_1998, author = {Meier, Christoph and Engel, Volker and Manthe, Uwe}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {07}, number = 1, pages = {36–41}, publisher = {{AIP} Publishing}, title = {An effective method for the quantum mechanical description of photoionization with ultrashort intense laser pulses}, volume = 109, year = 1998 }
• Photoelectron distributions from femtosecond pump/probe excitation with chirped probe pulses. Meyer, S.; Meier, C.; Engel, V. In The Journal of Chemical Physics, 108(18), S. 7631–7636. {AIP} Publishing, 1998.
  • [ BibTeX ]
  • [ DOI ]
  @article{Meyer1998, author = {Meyer, S. and Meier, C. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {05}, number = 18, pages = {7631–7636}, publisher = {{AIP} Publishing}, title = {Photoelectron distributions from femtosecond pump/probe excitation with chirped probe pulses}, volume = 108, year = 1998 }
• Fragmentation dynamics of Fe(CO)₅ upon femtosecond excitation: a time-dependent statistical description. Rubner, O; Engel, V. In Chemical Physics Letters, 293(5), S. 485–490. 1998.
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  • [ DOI ]
  @article{RUBNER1998485, author = {Rubner, O and Engel, V}, journal = {Chemical Physics Letters}, keywords = {myown}, number = 5, pages = {485 - 490}, title = {Fragmentation dynamics of Fe(CO)₅ upon femtosecond excitation: a time-dependent statistical description}, volume = 293, year = 1998 }
• Single-collision caging of dissociating I₂: wave packet calculations and simulation of femtosecond spectra. Meier, C; Engel, V; Beswick, J.A. In Chemical Physics Letters, 287(5-6), S. 487–495. Elsevier {BV}, 1998.
  • [ BibTeX ]
  • [ DOI ]
  @article{Meier1998, author = {Meier, C and Engel, V and Beswick, J.A}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {05}, number = {5-6}, pages = {487–495}, publisher = {Elsevier {BV}}, title = {Single-collision caging of dissociating I₂: wave packet calculations and simulation of femtosecond spectra}, volume = 287, year = 1998 }
• Pump/Probe Spectroscopy of NaI in Rare Gas Environments:  A Statistical Description. Dietz, H.; Engel, V. In The Journal of Physical Chemistry A, 102(38), S. 7406–7413. 1998.
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  @article{doi:10.1021/jp981890w, abstract = {A theoretical study of the femtosecond spectroscopy of the NaI predissociation process under high-pressure conditions is presented. We employ a statistical model to mimic the pressure dependence of pump/probe signals for different rare gases. The model uses an ensemble of trajectories to approximate the quantum dynamics of the wave packet, which is prepared by ultrashort pulse excitation. Predissociation is treated within the Landau−Zener model for curve crossing. Collisions are modeled as instantaneous events assuming hard sphere scattering. The collision probability is calculated statistically so that no adjustable parameter has to be introduced. The results show how coherent wave packet motion is influenced by scattering processes and how this is reflected in femtosecond pump/probe signals.}, author = {Dietz, H. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {myown}, number = 38, pages = {7406-7413}, title = {Pump/Probe Spectroscopy of NaI in Rare Gas Environments:  A Statistical Description}, volume = 102, year = 1998 }
• Molecular femtosecond excitation described within the Gaussian wave packet approximation. Braun, M.; Metiu, H.; Engel, V. In The Journal of Chemical Physics, 108(21), S. 8983–8988. {AIP} Publishing, 1998.
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  @article{Braun_1998, author = {Braun, M. and Metiu, H. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {06}, number = 21, pages = {8983–8988}, publisher = {{AIP} Publishing}, title = {Molecular femtosecond excitation described within the Gaussian wave packet approximation}, volume = 108, year = 1998 }
• Geminate recombination processes induced by rare gas collisions with predissociating NaI molecules prepared by femtosecond excitation. Dietz, H.; Engel, V. In Theoretical Chemistry Accounts, 100(1), S. 199–203. 1998.
  • [ BibTeX ]
  • [ DOI ]
  @article{Dietz1998, abstract = {NaI molecules predissociate after excitation with ultrashort pulses at a peak wavelength of 320 nm. In rare gas environments at higher pressures the process of geminate recombination is likely to occur. We studied the dynamics of these processes under various pressure conditions and for different collision partners. The calculations were performed within a three-dimensional statistical model which simulates the NaI wave-packet dynamics with classical trajectories and the collisions via an instantaneous hard-sphere scattering.}, author = {Dietz, H. and Engel, V.}, journal = {Theoretical Chemistry Accounts}, keywords = {myown}, month = 11, number = 1, pages = {199–203}, title = {Geminate recombination processes induced by rare gas collisions with predissociating NaI molecules prepared by femtosecond excitation}, volume = 100, year = 1998 }
• Femtosecond Time-Resolved CARS Spectroscopy on Binary Gas-Phase Mixtures:  A Theoretical and Experimental Study of the Benzene/Toluene System. Rubner, O.; Schmitt, M.; Knopp, G.; Materny, A.; Kiefer, W.; Engel, V. In The Journal of Physical Chemistry A, 102(48), S. 9734–9738. 1998.
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  @article{doi:10.1021/jp9832589, abstract = {Femtosecond time-resolved CARS measurements on benzene, toluene, and binary mixtures of these molecules have been performed in the gas phase. Whereas a two-pulse excitation process prepares benzene in a single vibrational state, a vibrational wave packet is excited in toluene, which gives rise to oscillatory patterns in the CARS signal. For the mixed system one finds beats between modes coherently excited in both molecules. The results are analyzed using perturbative quantum calculations. It is shown that the rotational degree of freedom is responsible for the decay of the CARS signal in all cases. Furthermore, it is demonstrated that the details of the excitation process have to be incorporated in the calculation to obtain the correct amplitudes of the oscillating signals.}, author = {Rubner, O. and Schmitt, M. and Knopp, G. and Materny, A. and Kiefer, W. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {myown}, number = 48, pages = {9734-9738}, title = {Femtosecond Time-Resolved CARS Spectroscopy on Binary Gas-Phase Mixtures:  A Theoretical and Experimental Study of the Benzene/Toluene System}, volume = 102, year = 1998 }

• Femtosecond time-resolved two-photon ionization spectroscopy of K₂. Schwoerer, H.; Pausch, R.; Heid, M.; Engel, V.; Kiefer, W. In The Journal of Chemical Physics, 107(23), S. 9749–9754. {AIP} Publishing, 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{Schwoerer_1997, author = {Schwoerer, H. and Pausch, R. and Heid, M. and Engel, V. and Kiefer, W.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = 12, number = 23, pages = {9749–9754}, publisher = {{AIP} Publishing}, title = {Femtosecond time-resolved two-photon ionization spectroscopy of K₂}, volume = 107, year = 1997 }
• Semiclassical photodissociation cross section for H₂O. Hüpper, Bruno; Eckhardt, Bruno; Engel, Volker. In Journal of Physics B: Atomic, Molecular and Optical Physics, 30(14), S. 3191. 1997.
  • [ BibTeX ]
  @article{0953-4075-30-14-012, abstract = {We investigate semiclassically the photodissociation of water in the first absorption band. Experimental absorption spectra show weak undulatory structures, which are related to the vibrational symmetric stretch motion on the excited ##IMG## [http://ej.iop.org/images/0953-4075/30/14/012/img7.gif] -state potential-energy surface (PES). Using the cycle expansion resummation we demonstrate that there are only small corrections due to other fundamental periodic orbits and negligible contributions from longer orbits. The error in the positions of the semiclassical resonances is of the same order or less as the variations when using different Born - Oppenheimer potential surfaces. For this light molecule the background term is strongly influenced by quantum effects. We discuss estimates for the importance of quantum corrections and a way to incorporate them.}, author = {Hüpper, Bruno and Eckhardt, Bruno and Engel, Volker}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, keywords = {myown}, number = 14, pages = 3191, title = {Semiclassical photodissociation cross section for H₂O}, volume = 30, year = 1997 }
• Inversion of Potential Energy Curves from Continuum Resonance Raman Scattering Data with the Help of a Reflection Principle. Eichelsdörfer, M.; Engel, V. In Journal of Raman Spectroscopy, 28(6), S. 427–431. John Wiley & Sons, Ltd., 1997.
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  @article{JRS:JRS127, abstract = {An inversion method is presented for diatomic potential curves of electronically excited states which are the intermediate states for continuum resonance Raman scattering processes. Assuming a parametric form of the potential, the parameters are directly given as a function of certain frequencies which can be taken from experimentally determined Raman profiles. The origin of the procedure is a reflection principle which states that the nodal structure of vibrational wavefunctions serving as initial or final states in the two-photon process is apparent in the Raman cross-section recorded as a function of excitation frequency. The Cl2 molecule is used as an illustrative example. © 1997 John Wiley & Sons, Ltd.}, author = {Eichelsdörfer, M. and Engel, V.}, journal = {Journal of Raman Spectroscopy}, keywords = {myown}, number = 6, pages = {427–431}, publisher = {John Wiley & Sons, Ltd.}, title = {Inversion of Potential Energy Curves from Continuum Resonance Raman Scattering Data with the Help of a Reflection Principle}, volume = 28, year = 1997 }
• The calculation of time-resolved negative-ion-to-neutral-to-positive-ion-spectra with an application to iron-carbonyl. Rubner, O.; Meier, C.; Engel, V. In The Journal of Chemical Physics, 107(4), S. 1066–1072. {AIP} Publishing, 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{Rubner1997, author = {Rubner, O. and Meier, C. and Engel, V.}, journal = {The Journal of Chemical Physics}, keywords = {myown}, month = {07}, number = 4, pages = {1066–1072}, publisher = {{AIP} Publishing}, title = {The calculation of time-resolved negative-ion-to-neutral-to-positive-ion-spectra with an application to iron-carbonyl}, volume = 107, year = 1997 }
• A theoretical analysis of the time-resolved femtosecond CARS spectrum of I₂. Meyer, S; Schmitt, M; Materny, A; Kiefer, W; Engel, V. In Chemical Physics Letters, 281(4-6), S. 332–336. Elsevier {BV}, 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{Meyer1997, author = {Meyer, S and Schmitt, M and Materny, A and Kiefer, W and Engel, V}, journal = {Chemical Physics Letters}, keywords = {myown}, month = 12, number = {4-6}, pages = {332–336}, publisher = {Elsevier {BV}}, title = {A theoretical analysis of the time-resolved femtosecond CARS spectrum of I₂}, volume = 281, year = 1997 }
• Vibrational Revivals and the Control of Photochemical Reactions. Meyer, S.; Engel, V. In The Journal of Physical Chemistry A, 101(42), S. 7749–7753. 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{doi:10.1021/jp971247u, abstract = {The short-time vibrational wave packet motion in a molecule with several vibrational degrees of freedom shows oscillatory behavior with the characteristic vibrational periods. For long times revivals will occur, i.e., the wave packet restores its initial form. For small vibrational coupling the revival times in the single modes are approximately those of the uncoupled nuclear motion. The fact that the revivals with respect to the single degrees of freedom occur at different times can be used to control the branching ratio between reaction channels by short-pulse electronic excitation at different times. A model of the HOD molecule is used to demonstrate this general scenario.}, author = {Meyer, S. and Engel, V.}, journal = {The Journal of Physical Chemistry A}, keywords = {myown}, number = 42, pages = {7749-7753}, title = {Vibrational Revivals and the Control of Photochemical Reactions}, volume = 101, year = 1997 }
• The perturbation of coherent wave-packet dynamics by atom/molecule collisions: the NaI + Ar system. Dietz, H.; Knopp, G.; Materny, A.; Engel, V. In Chemical Physics Letters, 275(5-6), S. 519–526. Elsevier {BV}, 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{Dietz1997, author = {Dietz, H. and Knopp, G. and Materny, A. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {09}, number = {5-6}, pages = {519–526}, publisher = {Elsevier {BV}}, title = {The perturbation of coherent wave-packet dynamics by atom/molecule collisions: the NaI + Ar system}, volume = 275, year = 1997 }
• Stimulated emission processes and strong field effects in ultrashort pulse excitation of a predissociative molecule. Dietz, H.; Materny, A.; Engel, V. In Chemical Physics, 217(2-3), S. 249–257. Elsevier {BV}, 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{Dietz1997, author = {Dietz, H. and Materny, A. and Engel, V.}, journal = {Chemical Physics}, keywords = {myown}, month = {05}, number = {2-3}, pages = {249–257}, publisher = {Elsevier {BV}}, title = {Stimulated emission processes and strong field effects in ultrashort pulse excitation of a predissociative molecule}, volume = 217, year = 1997 }
• Pump/probe direct photoionization from thermally hot samples: the Cs₂ molecule. Braun, M.; Engel, V. In Zeitschrift f{ü}r Physik D Atoms, Molecules and Clusters, 39(4), S. 301–307. 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{Braun1997, abstract = {We investigate the femtosecond photoionization of Cs2 within a model including four electronic states. A thermally broad initial state distribution influences the timedependence of the transient ion signals crucially. We show that even for the present case of simple one-dimensional motion the interpretation of ionization signals requires special care under certain experimental conditions. The results are compared to recent experimental data and a modified ionic state potential is constructed.}, author = {Braun, M. and Engel, V.}, journal = {Zeitschrift f{\"u}r Physik D Atoms, Molecules and Clusters}, keywords = {myown}, month = 12, number = 4, pages = {301–307}, title = {Pump/probe direct photoionization from thermally hot samples: the Cs₂ molecule}, volume = 39, year = 1997 }
• Vibrational dynamics and energy flow in a multi-mode organometallic compound. Markert, T.; Malisch, W.; Engel, V. In Chemical Physics Letters, 270(1-2), S. 222–228. Elsevier {BV}, 1997.
  • [ BibTeX ]
  • [ DOI ]
  @article{Markert1997, author = {Markert, T. and Malisch, W. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {05}, number = {1-2}, pages = {222–228}, publisher = {Elsevier {BV}}, title = {Vibrational dynamics and energy flow in a multi-mode organometallic compound}, volume = 270, year = 1997 }

• Wave-packet interference and stabilization of a predissociating molecule. Dietz, H.; Engel, V. In Chemical Physics Letters, 255(4-6), S. 258–262. Elsevier {BV}, 1996.
  • [ BibTeX ]
  • [ DOI ]
  @article{Dietz1996, author = {Dietz, H. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = {06}, number = {4-6}, pages = {258–262}, publisher = {Elsevier {BV}}, title = {Wave-packet interference and stabilization of a predissociating molecule}, volume = 255, year = 1996 }
• Short-time wave-packet dynamics and the reflection principle of continuum resonance Raman scattering. Eichelsd{ö}rfer, M.; Engel, V. In Chemical Physics Letters, 263(5), S. 640–644. Elsevier {BV}, 1996.
  • [ BibTeX ]
  • [ DOI ]
  @article{Eichelsdrfer1996, author = {Eichelsd\"{o}rfer, M. and Engel, V.}, journal = {Chemical Physics Letters}, keywords = {myown}, month = 12, number = 5, pages = {640–644}, publisher = {Elsevier {BV}}, title = {Short-time wave-packet dynamics and the reflection principle of continuum resonance Raman scattering}, volume = 263, year = 1996 }
• Addendum to: Nanosecond wave-packet propagation with the split-operator technique [Comput. Phys. Commun. 93 (1996) 152]. Dietz, H.; Braun, M.; Meier, C.; Engel, V. In Computer Physics Communications, 98(1-2), S. 265. Elsevier {BV}, 1996.
  • [ BibTeX ]
  • [ DOI ]
  @article{Dietz1996, author = {Dietz, H. and Braun, M. and Meier, C. and Engel, V.}, journal = {Computer Physics Communications}, keywords = {myown}, month = 10, number = {1-2}, pages = 265, publisher = {Elsevier {BV}}, title = {Addendum to: Nanosecond wave-packet propagation with the split-operator technique [Comput. Phys. Commun. 93 (1996) 152]}, volume = 98, year = 1996 }