A re-examination of thermal accommodation coefficient theory

Abstract

Contrary to accepted ideas, the first-order quantum-mechanical perturbation theory of Lennard-Jones and Devonshire (7) can give correct results for the energy transferred from a “high” energy gas atom to a solid surface which it hits, even though the creation of several phonons simultaneously in the solid is required. Simple models are used to show that Landau's continuum model leads to a factor of two error for high energy (“hard”) impacts, that the consideration by D evonshire of an internal lattice atom in place of a surface atom leads to error except for hard impacts, and that the use by Zwanzig (8) and by Cabrera (14) of one-dimensional models leads to a commonly-held fallacy when the gas atom is heavier than the lattice atoms, as shown also by Goodman. (18) It is further shown from the work of Miller and Pursey (16, 17) that surface modes, which are not considered in existing accommodation coefficient theories, may augment the energy transfer by a factor of three or more. The impact energies are considered to be well below the sputtering threshold to allow linearization of the interactions between lattice atoms.