Berlin 2001 – wissenschaftliches Programm
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MO: Molekülphysik
MO 15: Post-Deadline Contributions Molecular Physics
MO 15.1: Poster
Freitag, 6. April 2001, 12:30–15:00, AT3
Internal Conversion among the Singlet States of β-Carotene: Pathways with the Highest Conversion Rates — •Torsten Siebert, Michael Schmitt, Tao Chen, Arnulf Materny, and Wolfgang Kiefer — Institut für Physikalische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
The ultrafast internal conversion (IC) between the second and first electronically excited singlet states as well as the IC to the electronic ground state of β-carotene plays a primary role in the mechanism with which this molecule functions as auxiliary pigment in photosynthesis. In order to investigate the S2/S1 and S1/S0 IC, femtosecond time-resolved transient population gratings were induced into solutions of β-carotene by means of two independent laser pulses, which pump the S2 state. This grating was interrogated by scattering a third, time-variable probe pulse on the grating under Bragg conditions. By tuning the probe laser resonant to the S1 absorption, it was possible to observe the development in the S1 population and with this, the S2/S1 as well as S1/S0 IC. In order to monitor the population in different regions on the S1 state potential, the broadband signal was spectrally resolved and the wavelength of the probe pulse was varied to include spectral positions red-shifted to the S1 absorption. The measurements show, that the rates of IC are strongly dependent on the region of the potential that is monitored. An analysis allows for pathways with maximal conversion rates to be identified and the results are discussed with regard to the function of carotenoids in light-harvesting systems.