A structural study of the interaction of SO2 with Cu(111)

The technique of chemical-shift normal-incidence X-ray standing waves (CS-N IXSW) has been applied to a study of the interaction of SO2 with Cu(111), y ielding quantitative information on the local adsorption geometry of adsorb ed SO2 at low temperature and coadsorbed atomic sulfur with an SOx species, identified on the basis of near-edge X-ray absorption fine structure (NEXA FS) as SO3. Atomic sulfur appears to occupy a mixture of face-centred cubic and hexagonal close-packed hollow sites, while the SO3 species adsorbs wit h its C-3v axis perpendicular to the surface atop a surface copper atom wit h the S-O bonds out of plane such that the oxygen atoms are closer to the s urface: there appears to be some local distortion of the outermost copper l ayers around this species. While SO2 is found to adsorb with its molecular plane essentially perpendicular to the surface? and the data are most readi ly interpreted in terms of a bridging geometry bonding through the oxygen a toms, there are marked inconsistencies between these results and those of a n earlier surface extended XAFS (SEXAFS) investigation of this species on C u(111), and alternative interpretations are discussed. (C) 2000 Elsevier Sc ience B.V. All rights reserved.