Semiclassical treatment of reactions at surfaces with electronic transitions

The semiclassical treatment of reactions at surfaces with electronic transi tions based on the fewest-switches algorithm is compared with full quantum mechanical results. As a model system the ionization probability in I-2 sca ttering from a diamond surface is chosen. In the calculations we treat the molecular distance from the surface and one surface oscillator coordinate e xplicitly. Furthermore, we also consider molecular rotation in the semiclas sical calculations. The semiclassical results agree with the quantum result s although some discrepancies remain, as far as the phase coherence is conc erned. We identify energy transfer to molecular and surface degrees of free dom as a possible mechanism that could explain the experimental dependence of the ionization probability on the incident kinetic energy of the molecul e.