Chemisorption of dioxygen on the Ag(110) surface

Abstract

We have explored the chemisorption of molecular O2 at the long bridge site on the Ag(110) surface using a 24 atom ‘‘supercell’’ cluster model for the Ag(110) surface. From first principles generalized valence bond and configuration interaction calculations, we find that for chemisorption at this site, orientation of the O2 molecular axis along a [11̄0] azimuth is greatly preferred. In this orientation, we find geometric and spectroscopic parameters that are in excellent agreement with available experimental measurements. The molecule is found to sit 0.94 Å above the surface, with an O–O bond distance of 1.55 Å, and vibrational frequencies of ν(O–O)=627 cm−1 and ν⊥=278 cm−1. The O2 π orbitals normal to the surface interact strongly with second layer Ag atoms, while π orbitals parallel to the surface interact with first layer Ag atoms. Charge transfer is extensive (≊1.0–1.5 electrons) at the equilibrium geometry. The O2 is found to bond to an excited state of the Ag24 cluster when in the preferred geometry, and as a result, is endothermic with respect to the cluster ground state. We estimate the true bond energy on an Ag(110) surface to be 11.1 kcal/mol.