Quasimolecular stable forms of oxygen on silver surface. Theoretical analysis by the density functional theory method

A quantum chemical investigation of possible associative oxygen forms on de fective silver surface has been performed with the use of gradient-correcte d density functional theory (DFT) in the cluster approximation. A surface d efect was simulated by a cation vacancy (V). Cluster models (M1: Ag12 and M 2: O3Ag12) of an active adsorption site (AS) with a vacancy were chosen on the basis of the structure of high-temperature layered silver oxide. The ad sorbed layer on the defective surface was simulated by three oxygen atoms. For the atomic and associative (molecular) forms, the computations gave two stable structures of the adsorbed layer with C-3V and C-2V symmetry. The q uasimolecular C-2V structure -Ag-O-O-ep-O-Ag- resembling metal ozonides is by 44 kcal/mol more stable than the atomic C-3V structure. The C-2V structu re is singlet and has an electrophilic epoxidizing oxygen atom O-ep. A theo retical estimation of the density of states (DOS) in the quasimolecular oxy gen form revealed a complex structure below the 4d band. Additional DOS pea ks in this region are due to associative O-O bonds. (C) 2000 Elsevier Scien ce B.V. All rights reserved.