Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 48: Surface dynamics I
O 48.7: Vortrag
Mittwoch, 24. März 2010, 12:00–12:15, H40
Ultrafast electron dynamics at alkali-ice interfaces probed with two-photon photoemission — •Michael Meyer1, Mathieu Bertin2, Uwe Bovensiepen3, and Martin Wolf1 — 1Freie Universität Berlin, FB Physik, 14195 Berlin, Germany — 2LPMAA, Université Pierre et Marie Curie, 75252 Paris cedex 05, France — 3Fakultät für Physik, Universität Duisburg-Essen, 47048 Duisburg, Germany
An excess charge in a polar environment, i.e. an electron or an ion, is known to form a charge-solvent complex. This process involves a re-orientation of the molecules surrounding the charge, resulting in the screening of the extra charge and in the increase of its binding energy. Following earlier work, which investigated the dynamics of such solvated electrons in amorphous D2O/Cu(111) by time-resolved two-photon photoemission, we analyze here the influence of coadsorbed sodium ions. In amorphous ice multilayers these electrons are located in the bulk of the ice film. After adsorption of sub-monolayer coverages of sodium ions a new species of solvated electrons is observed. By titration experiments using Xe overlayers we can demonstrate that the binding site of these electrons is located at the ice/vacuum-interface. Depending on the sodium coverage the lifetime of the excited electrons in this state is up to ten picoseconds, which is more than one order of magnitude longer compared to solvated electrons in amorphous water ice on Cu(111). The energetic stabilization rate of around 800 meV/ps is almost three times higher than in the case without sodium. The observed state can be attributed to excess electrons located at the alkali ions residing at the ice/vacuum-interface.