Correction to the Devonshire Theory of Accommodation Coefficients for Bound-State Transitions in Gas–Surface Interactions

Abstract

A calculation is presented of the bound-state correction to the quantum mechanical theory (that is, the Devonshire theory) of energy accommodation coefficients (a.c.); this correction takes account of transitions of gas atoms into bound states at the solid surface. Using certain simplifications which are easily interpreted physically, bound-state analogs of the Devonshire formula are presented. Although the treatment is one-dimensional throughout, the corrected theory is compared with experimental data on the a.c. of He–W as a function of temperature T. It is concluded that the bound-state correction improves considerably the agreement with experiment obtained by Roach and Harris using their modified Devonshire formula, although there is still some disagreement, at both high and low T. The theoretical a.c., even after correction, vanishes at T = 0, in disagreement with present experimental trends; a plea is made for further experiments to help resolve this point.