On the nonequilibrium distribution of adatoms resulting from dissociative adsorption of a diatomic gas

Abstract

Kinetic equations governing the distribution of adatoms resulting from irreversible, dissociative adsorption of homonuclear diatoms onto a two-dimensional lattice are derived. Desorption and atomic skating are ignored, which allows the problem to be conveniently formulated from a molecular viewpoint. The rate constant for adsorption is assumed to be of an Arrhenius form with an activation energy which consists of an additive contribution from the interaction of the adsorbing molecule with each adatom on the surface. Special attention is paid to the relationship between the molecular distribution resulting from irreversible adsorption and the equilibrium molecular distribution. The kinetic equations are solved as a power series in the covering fraction; the coefficients involve molecular cluster diagrams similar to those in equilibrium, virial expansions. Comparison of the nonequilibrium and equilibrium covering fraction expansions of the molecular pair distribution functions is made, and an illustrated example is considered for a case where the functions and their expansions can be evaluated exactly. Finally, the effect of the nonequilibrium distribution of adatoms on the configurational contribution to the thermodynamic properties of the adsorbate is discussed.