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MO: Fachverband Molekülphysik

MO 9: Femtosecond Spectroscopy II

MO 9.8: Talk

Tuesday, March 15, 2011, 12:30–12:45, TOE 317

Excited state vibrational coherence dynamics of all-trans retinal protonated Schiff-bases investigated with (Pump-)DFWM — •Jan Philip Kraack, Tiago Buckup, and Marcus Motzkus — Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany

The retinal chromophore performs as a key-element in various biological mechanisms such as vision or bacterial photosynthesis. Photon-absorption induces an ultrafast double-bond isomerization, the decisive steps of which still remain to be understood to date. Special attention has recently been attracted by excited state low-frequency vibrational coherences[1]. Particularly, the understanding of their impact on the isomerization and their mechanism of induction are expected to pave the way for a complete understanding of the dynamics. Using Pump Degenerate Four-Wave-Mixing (Pump DFWM)[2], we show that such coherences are activated through coherent internal vibrational energy redistribution. This process requires only low excess photon energy for excitation, contrasting previous assertions[1]. Pump DFWM also reveals that, besides their strongly damped time-evolution, excited state coherences can only be observed in a narrow time window after excitation. The results are discussed in terms of a relaxation model comprising contributions from two close-lying excited electronic states.

[1] G. Zgrablic, S. Haacke, and M. Chergui, Chemical Physics 338, 168 (2007)

[2] J. Hauer, T. Buckup, and M. Motzkus, Journal of Physical Chemistry A 111, 10517 (2007)