Adsorption and disproportionation reaction of OH on Ag surfaces: dipped adcluster model study

The adsorption and surface disproportionation reactions of OH on various si lver surfaces were studied by the dipped adcluster model (DAM) combined wit h ab initio HF and MP2 methods. Our studies show that OI-I binds strongly t o Ag surfaces; the adsorption energies were calculated to be 118.3 kcal mol (-1) at the short bridge site on Ag(110), 108.6 kcal mol(-1) at the fourfol d hollow site on Ag(100), and 97.3 kcal mol(-1) at the threefold hollow sit e on Ag(111). The H-O axis is preferentially perpendicular to the surface f or OH on Ag(100) and Ag(111), but tilts about 50 degrees along the [001] az imuthal orientation on Ag(110). The Ag 4d orbital plays an important role i n adsorbing OH, whose molecular orbital analysis is described. Coadsorption of OH at the nearest fourfold sites on Ag(100) is stable with the H-O axis perpendicular to the surface; an inclined OH structure is proposed for the coadsorption of OH at the bridge sites and it is shown to be very reactive regarding the surface disproportionation reaction of OH. The structures an d energy surfaces for the disproportionation reaction of OH to form H2O on Ag(100) are presented. The present study provides clear information regardi ng the adsorption, coadsorption and disproportionation of OH on Ag surfaces . (C) 1999 Elsevier Science B.V. All rights reserved.