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.