Calculations of 1 eV–3 keV oxygen scattering from Ag(111) usingab initiopair potentials

Abstract

Classical trajectory calculations, using an ab initio Ag–O potential, are presented of O2 scattering from Ag(111) in a broad energy range. These calculations can explain the results of various O2/Ag(111) scattering experiments performed at different energies. For O2 scattering around 1 eV, the experimentally observed angular broadening in the scattered signal can be explained as an onset of surface rainbows. The degree of dissociation observed in scattering around 200 eV (incoming angle with respect to surface normal (θi=70°) and around 2 keV θi=85°) can be explained by a collision-induced dissociation. Since O2/Ag(111) is a very corrugated system, we also studied the effect of the parallel velocity on the scattering. With constant normal velocity, the ‘‘largest corrugation’’ (most energy loss and dissociation) occurs for θi between 30° and 60°. For grazing incidence (θi≊85°), the scattering shows the characteristics of scattering from a flat surface: energy losses only decrease the normal component of the incident velocity and energy losses and fractions of dissociated molecules are independent of the parallel component. However, the molecule gets more rotationally excited than in the case of scattering from a flat surface with the same normal incident velocity. Finally, we investigated the relative amounts of vibrational and rotational excitation leading to dissociation. For a flat surface, the dissociation turns out to be mostly due to vibrational excitation, but for a corrugated surface, also rotational excitation largely contributes to dissociation.