Three-dimensional hard spheres theory of scattering of gas atoms from a solid surface I. Limit of large incident speed

Abstract

The results of analysis of a three-dimensional model of the interaction of monatomic gases with solid surfaces, a preliminary record of which was presented at the Fifth Rarefied Gas Dynamics Symposium, are presented in some detail. The model represents the solid surface atoms by similar, non-interacting, spheres, the centres of which form initially a regular two-dimensional array, and the gas atom by a sphere incident on this array. Collisions between the gas atom and the surface atoms obey the laws of classical hard spheres. The theory is restricted to the limit of large speed of the incident gas atoms; for example, the attractive forces between the gas atoms and the solid are neglected. The closely-related problems of (i) the detailed velocity distribution of the gas atoms reflected from the surface, (ii) the energy and momentum accommodation coefficients and (iii) the forces exerted on a target by a directed gas beam, are discussed and illustrated by means of examples selected from a comprehensive set of results; general qualitative trends relevant to these problems are evident.