Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 31: Surface Chemical Reactions and Heterogeneous Catalysis I

O 31.4: Talk

Tuesday, March 27, 2007, 16:30–16:45, H38

Local investigation of femtosecond laser induced processes: CO on Cu(111) — •Michael Mehlhorn, Heiko Gawronski, and Karina Morgenstern — Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2, D-30167 Hannover, Germany

A combination of femtosecond laser excitation with a low temperature scanning tunneling microscope is used to study two key processes, diffusion and close approach of reactants, of a non-adiabatic surface reaction for adsorbed CO molecules on a Cu(111) surface in real space. For the first process we obtain two different electron mediated excitation pathes by analyzing the dependence of the hopping rate of individual molecules on laser fluence. The first one involves inelastic scattering of one photo-excited substrate electron on the CO molecule whereas for the second process thermalized substrate electrons play the major role. For the second key process we investigate the generation of CO dimers. Femtosecond laser excitation leads to a transient attraction of usually repelling CO molecules. We model both processes quantitatively and extract a diffusion barrier of 87 meV and a CO-attraction energy of 30 meV.