Electronic excitation and quenching of atoms at insulator surfaces

A semiclassical method is employed for dynamical calculations of electronic transitions in collisions of gas atoms with insulator surfaces. The theory is based upon combining Micha’s self-consistent eikonal method (SCEM) with a stochastic reduction of the equations of motion for the condensed phase as represented in a generalized Langevin equation (GLE). The merged theory provides a framework that manifests the attractive computational advantages of both the SCEM and GLE modeling methods and can be readily applied to many modern problems involving electronically inelastic gas/surface collisions. The theoretical approach is numerically illustrated for a simple two-electronic-state curve crossing problem, where the effects of model parameters, surface temperature, and collision energy upon transition probabilities and energy accommodation are examined. For the model system studied the loss of energy of the gas atom into the surface is appreciable with pronounced effects depending upon the electronic transition probabilities. In collisions with a rigid model of the surface the transition probabilities exhibit Stückelberg oscillations as a function of the translational energy. These oscillations are ‘‘washed out’’ by the thermal effects of the surface at finite temperatures. The effect of electronic inelasticity can, however, be seen in the magnitudes of finite temperature energy transfers.