Application of a one-dimensional classical model of atom-oscillator scattering to atom-surface accommodation coefficient theory

A simplified model is presented for classical-mechanical calculation of the energy accommodation coefficient in gas-surface scattering: conservation of the tangential component of momentum of a gas atom is assumed, allowing restriction to a consideration of the changes in only the normal component of momentum, and the solid is represented by a single atom joined by a harmonic spring to a rigid wall; the gas atom-solid atom interaction is modelled by a (different) harmonic spring, the force-constant of which depends on the gas temperature. The model was devised to help point a way to solving some of the outstanding problems in more realistic (lattice) models: one major problem is the existence or non-existence of thermal equilibrium of a gas and a surface if their temperatures are equal, and another is the handling of the phenomenon of trapping, or sticking, of a gas atom at a surface. Some light is shed on both of these (and on some other) problems. Wherever possible, comparison is made with the best available experimental data.