The role of electron transfer processes in determining desorption kinetics

Abstract

The desorption step of heterogeneous processes taking place on solid–gas interfaces may be influenced by the bulk conductivity of the solid. This might be seen in systems where, during adsorption, negative charge is transferred to adsorbed species, leaving a positive hole. If the n-type conduction of the solid is high, then this hole may be filled by an electron, not from the adsorbed species but from the bulk of the solid. Desorption is thus shown to be a second-order process necessitating, apart from the adsorbed species, electronically vacant sites. Application of transition-state theory shows that the second-order desorption of monomolecular processes should appear at sufficiently low pressures, while at higher ones normal first-order kinetics applies.