| Abstract
| - In this paper we explain the wavelength-dependent oscillatory features in the pump−probe kinetics of thecore LH1 antenna of Rhodopseudomonas viridis (Monshouwer, R.; Baltuška, A.; van Mourik, F.; van Grondelle,R. J. Phys. Chem. A 1998, 102, 4360). A quantitative fit of the data was obtained using the doorway−window representation of the nonlinear optical response in the vibrational eigenstate basis. In contrast toLH1/LH2 complexes from the BChl a-containing species, the LH1 antenna of Rps. viridis is characterized bya strong coupling of the excitonic states with two underdamped low-frequency modes (58 and 110 cm-1 at77 K). Following a short femtosecond excitation pulse, this gives rise to the intense oscillations observed inthe pump−probe traces, including their time and excitation/detection wavelength dependence. Furthermore,it leads to a pronounced and specific heterogeneity of the major absorption band due to the combined effectsof the exciton splitting, disorder, and the presence of vibrational sidebands. The sharp maxima in the secondderivative of the low-temperature absorption spectrum (Monshouwer, R.; Visschers, R. W.; van Mourik, F.;Freiberg, A.; van Grondelle, R. Biochim. Biophys. Acta1995, 1229, 373) were assigned to the lowest exciton−vibrational transitions. The wavelength dependence of the experimentally observed oscillatory pattern suggestsa different vibrational coherence decay for the ground- and excited-state wave packets. This can be explainedby assuming the (incoherent) migration of the delocalized exciton (polaron) around the ringlike antenna witha characteristic time constant of 0.9−1.5 ps at 77K.
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