The Interplay of Energy Disposal and Reaction Rates in Exoergic Processes at Metal Surfaces: Desorption Rates in Vibrationally Excited Adlayers

Abstract

Abstract We report on the desorption kinetics of adsorbates from metal surfaces in the presence of exoergic-processes, either atom recombination or non-dissociative adsorption. The modeling takes into account the dissipation of the adatom energy to both the solid and the adlayer and permits one to investigate the effect of these processes on the desorption rate. The model kinetics, which is solved analytically for two recombination channels under non steady state conditions, shows that the desorption rate is ruled by the ratio between the rate constant for recombination and for energy loss to the solid. The behavior of the vibrational distribution function of the adatoms on this control parameter is analyzed and compared with Boltzmann equilibrium distributions. Rate coefficients for energy disposal to a metal surface, evaluated for a relaxation process involving electron-hole pair excitation, are shown to be linked to the electron density, which than becomes a control parameter of reaction rates at metal surfaces.