The sticking probabilities of gases chemisorbed on the surfaces of solids

Abstract

A theory of the sticking probability is presented which differs from those in the literature in that the rates of migration and desorption for physisorbed molecules when they are above sites occupied by chemisorbed molecules are not assumed to be equal to these rates when they are above unoccupied sites for chemisorption. It is shown that this treatment, without invoking surface heterogeneity, has some of the flexibility of that of E hrlich, which assumes a surface on which there are regions of high sticking probability and regions of negligible sticking probability. The present approach does not have the difficulty inherent in E hrlich's model in explaining a surface density of adsorbed atoms nearly equal to the surface density of the atoms of the substrate. The expression thus derived for the sticking probability as a function of coverage is compared with data from the literature for nitrogen on tungsten.