Energy exchange between inert gas atoms and a solid surface

Abstract 1. Introduction. — If gas atoms, having energy corresponding to a temperature T2, are incident on a solid surface at a temperature T1, then the reflected atoms will have a mean energy corresponding to some new temperature T2', which is a function of T1 and T2. For simplicity it is convenient to define Knudsen’s thermal accommodation coefficient as α = lim T1 → T2 → T T'2 - T2 / T1 - T2. The accommodation coefficient depends on the nature of the gas atom, the nature of the solid surface, and the temperature T. Accommodation coefficients have been measured by various workers, and the present paper is an attempt to give a theoretical explanation of the results of Roberts, who has measured the accommodation coefficient for helium on tungsten at various temperatures, taking particular precautions to obtain a clean surface.