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MO: Molekülphysik

MO 31: Ultrafast Photochemistry

MO 31.6: Talk

Monday, March 7, 2005, 11:45–12:00, HU 2091

Femtosecond dynamics of an aqueous fluoride CTTS system — •Hristo Iglev and Alfred Laubereau — Physik-Department E11, Technische Universität München, James-Franck-Straße, 85748 Garching

We report on the ultrafast electron photodetachment of concentrated aqueous electrolyte solutions at room temperature. The relaxation dynamics after two-photon excitation at 310 nm of the fluoride anion is studied by polarization-resolved pump-probe absorption spectroscopy in the VIS and NIR with 100 fs temporal resolution. Evidence is found for internal conversion within the CTTS manifold on a time scale of 380 fs proceeding to an intermediate level assigned to the lowest charge transfer state in a non-equilibrated solvation layer. The subsequent rearrangement of the water molecules around the new charge distribution acompanies the separation of the excess electron from the parent atom. Different to previous studies on other halides, an evidence is obtained that the quantum yield of the process is reduced by several ten percent by internal conversion to the fluoride ground level. Our results are consistent with the physical picture that a solvated electron:halogen atom pair is formed. The electron detachment to the final solvated electron competes with direct geminate recombination, so that approximately 23