Hannover 2010 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 7: Poster: Femtosecond Spectroscopy
MO 7.5: Poster
Dienstag, 9. März 2010, 16:00–18:30, Lichthof
Detailed simulation of time-resolved four wave mixing in carotenoids using the Brownian oscillator model — •Marie Marek1,2, Tiago Buckup1,2, and Marcus Motzkus1,2 — 1Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany — 2Physikalische Chemie, Philipps-Universität, D-35043 Marburg, Germany
Degenerate four wave mixing (DFWM) is an ideal technique for the simultaneous investigation of population and vibrational dynamics in complex molecular systems. However, for the interpretation of the four wave mixing signal a firm theoretical support is crucial due to the various processes contributing to the signal generation. In this work we develop systematically a fitting and simulation tool for DFWM based on the Brownian oscillator model. Depending on the underlying model and the investigated system up to 80 different interactions can be considered. We demonstrate our approach by fitting the signal of several carotenoids using an evolutionary algorithm, which allows for the testing of several rate models describing the carotenoids relaxation pathways. The best agreement is obtained with a simple model containing only S2, S1 and S0 with the respective lifetimes known from literature. Furthermore, our fitting procedure permits to determine the ratio of the involved transition dipole moments. Finally, we extend the simulations to pump-DFWM by introducing a population shift generated by the initial pump pulse and then calculating the DFWM signal on the excited state. By this means we confirm the involvement of a low-lying vibrationally hot state in the deactivation process of carotenoids.