Chemisorption of O-2 on Ag(110)

The interaction of O-2 with Ag(110) provides a classic example of precursor-mediated dissociation, with a well-characterised molecular state existing between the gas-phase molecule and the dissociated O atoms. Results are presented of plane-wave, pseudopotential calculations of the structure and energy of the chemisorbed O atom and O-2 molecule. For the O atom only small differences are found in the binding energy for adsorption into different high-symmetry sites in the surface channels. For the O-2 molecule the preferred adsorption site is found to be the four-fold hollow, with a binding energy of 0.5 eV, although there is no clear preference for the orientation of the molecular axis either parallel or perpendicular to the surface channels. Both geometries involve considerable disturbances of the surface and sub-surface sliver atoms. Analysis of the electronic structure shows filling of the oxygen 1 pi g* (anti-bonding) orbital, and polarisation of the oxygen molecule and surface silver atoms. The chemisorbed state shows negligible spin polarisation.