Theoretical study of gas–solid energy transfer: An isotropic Debye model

Abstract

We present a model calculation for gas–solid energy transfer in which the solid is approximated as an isotropic Debye solid. For a given initial state of the solid (described by phonon occupation numbers), only states differing from this arbitrary initial state by one phonon (created or destroyed in an arbitrary state) are included in the basis set describing the solid. Using this basis set, a close-coupling calculation is carried out describing energy transfer during a gas–solid collision. Since the scattering calculation does not employ perturbation, all states in the basis set are coupled. Averages over phonon momenta and directions are carried out before the calculation, which results in considerable simplification. Comparisons are made with He+Ag(111) experimental results. Qualitative agreement is good, and quantitative agreement is within a factor of 2. Our model tends to underestimate inelastic effects. The importance of kinematic and geometric considerations is stressed.