COMPARISON OF APPROXIMATION METHODS FOR INELASTIC GAS SURFACE SCATTERING WITH EXACT RESULTS

Two different approximation schemes are used to calculate the energy transfer of gas particles scattered inelastically at solid surfaces. The average energy ΔE exchanged between translational and rotational degrees of freedom of diatomic molecules is evaluated within the distorted-wave Born approximation. We show that, for linear coupling, the first order DWBA results for ΔE are correct although the final state distribution (due to higher order contributions) may be totally wrong. Concerning the energy distribution we consider both phonon and rotational excitation in the framework of semiclassical methods. The sudden approximation considers the (vibrational or rotational) variables as being fixed during the scattering process. We incorporate their unperturbed motion and obtain better agreement with coupled-channel calculations. © 1990.