Properties of adsorbed oxygen forms on a defective ag(111) surface. DFT analysis

Abstract

A cluster model of an Ag12–3O (ASV) adsorption center using layered silver oxide as a prototype is proposed. The model includes a cation vacancy V on the Ag(111) surface and oxide type subsurface oxygen atoms Oox. Density functional theory (DFT) (B3LYP/LANL1MB approximation) is used to analyze the electronic structure of ASV and oxygen adsorption on this center, ASV+O → AS–O. As shown by the calculations, the adsorbed oxygen is associated with the subsurface oxygen atoms Oss to form structures similar to metal ozonides — Ag–Oss–Oep–Oss–Ag–Oox–Ag, containing electrophilic oxygen Oep along with the oxide oxygen Oox. The optical spectra of the ASV and AS–O centers were calculated by the configuration interaction method with single excitations (CIS). For ASV, the most intense absorption bands were obtained in the region 500-700 nm. Oxygen association is accompanied by a sharp decrease in spectrum intensity in the range 600-700 nm and an increase in the intensity of the peak at 500 nm. Vibration frequencies and (IR) intensities were determined for the ASV and AS–O centers. The ASV center exhibits a characteristic spectrum in the region 350-500 cm–1, which corresponds to the frequency spectrum of the surface oxide Ag2O. For associated oxygen forms (AS–O center), the calculations predict additional peaks around 980, 640 and 230 cm–1. These peaks are due to the vibrations of the Oss–Oep–Oss structural unit, stabilized at the cation vacancy.