The kinetics of H₂ dissociative chemisorption: The role of transient

Abstract

The Lee-DePristo model for the dissociative chemisorption of H₂ on Ni(100) has an interesting behavior. The potential energy surface has a minimum corresponding to a molecular, physisorbed state. This minimum is shallow and at 300 K the lifetime of physisorbed H₂ is extremely short. One is then justified in treating the kinetics as a direct dissociation and ignoring physisorption. At 100 K physisorbed H₂ has a long lifetime and one is forced to consider a two-step kinetics: H₂ is first physisorbed and then dissociated. While chemical kinetics describes easily these two limiting cases, it offers little guidance for the intermediate temperature. We show here how the correlation function theory deals with this situation by providing equations which cover all temperature regimes. The theory is general and can be used in all cases when intermediates with shallow wells participate in the reaction mechanism.