Model studies of oxygen chemisorption on silver surfaces using an AgO₂ cluster

Abstract

Ab initio all electron SCF calculations have been carried out on low lying states of AgO₂ of C_s and C _2v symmetry, and on OAgO of D _∞h symmetry, and the results are related to the observed chemisorption properties of dioxygen on silver surfaces. Analytic second derivatives were used to characterize the stationary points on the potential energy surfaces and to obtain harmonic frequencies to compare with the results of electron energy loss spectra. The C_s species are shown to be true minima and a bonding mechanism is proposed which explains the unique stability observed experimentally for the ‘out of plane’ chemisorbed state of dioxygen on Ag(111). Calculations on the C _2v species show these to be transition states for interconversion of the relevant C_s species. While the OAgO species is shown to be unstable, the shallow curvature of the potential energy surface would indicate that on an extended silver surface, dissociation of the dioxygen would be expected, as recently proposed by McKee. The relevance of the current calculations to the interpretation of spectra from matrix isolated silver-dioxygen complexes is also discussed.