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MO: Fachverband Molekülphysik

MO 4: Femtosekundenspektroskopie II

MO 4.6: Talk

Monday, March 10, 2008, 17:45–18:00, 3G

Determination of electronic transition dipole moment orientations by polarization re-solved femtosecond VIS-pump / IR-probe spectroscopy — Martin Linke, Moritz Theisen, Alexandra Lauer, Henk Fidder, and •Karsten Heyne — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany

Excitation of an isotropic ensemble of molecules with linear polarized light pulses leads to an anisotropic distribution of excited molecules (photoselection). During anisotropy decay conformational changes and the orientation of transition dipole moments can be identified by femtosecond polarization resolved pump-probe experiments. We determined the orientations of electronic and infrared transition dipole moments of Coumarin 314 and of Chlorophyll a molecules in solution.

The orientation of the electronic transition dipole moment of the Qy band within the molecular structure of Chlorophyll a is the basis for simulating many properties of photosynthetic systems. Determinations thus far of the electronic transition dipole moment orientations of Chlorophyll a were made on oriented samples with steady state spectroscopy, and with steady state anisotropy experiments. These experiments yielded angles for the orientation of the Qy electronic transition dipole moment with respect to the x-axis varying from 70° to 90°. Using polarization resolved VIS pump / IR-probe experiments we reinvestigated this issue.