Chemisorption of carbon monoxide on tungsten. Part 2.—Lateral interaction model for desorption kinetics

Abstract

Ordered structures formed by the β states of carbon monoxide on single crystal tungsten surfaces imply strong lateral interactions between adatoms. A statistical model, based on the quasi-chemical approach of Fowler and Guggenheim, is used to derive a kinetic equation for the associative desorption of a heteronuclear diatomic molecule, taking into account the existence of lateral interactions between nearest-neighbour adatoms in the overlayer. The model thus provides a link between structural and kinetic studies of chemisorption. It is successfully applied to the β desorption spectra for CO on W reported in Part 1, and a pairwise lateral repulsive interaction energy of 20 kJ mol^–1 between C and O adatoms is derived. The kinetic equation is extended to allow for a variation in the C/O adatom ratio, and again the predictions of the model are in close agreement with the experimental CO desorption spectra of Goymour and King from mixed O₂+ CO adlayers on W.