Molecular and atomic oxygen on unpromoted and cesium promoted Ag(111) surfaces

Using density functional theory, the energetics of chemisorption and dissociation are computed for molecular oxygen on an unpromoted and a cesium promoted cluster model of the reduced [111] surface of silver. The computed barriers and thermochemistry for our model clusters suggest that dissociation on unpromoted Ag(111) surfaces is activated, but thermochemically favored. Our computed barrier heights and product energies for the unpromoted silver cluster are compared with experimental data. The activation energy for dissociation on the cesium promoted surface shows a cesium coverage dependence, but, again the dissociated product is thermochemically favored. Atomic charges on all atoms were computed for both the unpromoted and promoted cluster models. Analysis of the atomic charges indicates that cesium acts as an electron donor to the silver cluster and that oxygen extracts a portion of the donated electron density from the cluster.