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MO: Fachverband Molekülphysik

MO 3: Femtosekundenspektroskopie I

MO 3.4: Talk

Monday, March 10, 2008, 15:00–15:15, 3G

Direct Femtosecond Observation of Tight and Loose Ion Pairs upon Photoinduced Bimolecular Electron Transfer — •Katrin Adamczyk¹, Omar F. Mohammed², Natalie Banerji², Jens Dreyer¹, Bernhard Lang², Erik T. J. Nibbering¹, and Eric Vauthey² — ¹Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany — ²Department of Physical Chemistry, University of Geneva, 30 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland

Photoinduced bimolecular electron transfer reactions have been subject of intensive chemical dynamics research for many decades [1]. These processes play a key role in many areas of chemistry and biology, among these are photosynthesis, solar energy conversion, ET in proteins and biocatalysis. Generally accepted models suppose that charge separation in polar solvents leads to two geminate ion pairs, namely loose or solvent-separated ion pairs (LIPs) and tight or contact ion pairs (TIPs). We show that monitoring marker modes of the ion products [2] with polarisation-sensitive ultrafast infrared spectroscopy enables a differentiation of the contributions of these distinct ion pairs in the observed kinetics. We find that large exergonic electron transfer reactions predominantly occur in tight donor-acceptor pairs. Tight ion pairs are found to be highly anisotropic, revealing the importance of mutual orientation of the reactants and thus demanding refinement of theoretical models relying on spherical reaction species that solely involve reaction distances. [1] A. Weller, Pure Appl. Chem. 54, 1885 (1982). [2] O. F. Mohammed et al., J. Phys. Chem. A 110, 13676 (2006).