The adsorption site and orientation of CH3S on Ni(111)

The angle-resolved X-ray photoelectron spectra for 0.15 monolayers (ML) of sulfur, and 0.25 ML methyl thiolate formed at 100 K and annealed to 150 and 250 K, on Ni(lll) are analyzed to determine the structures of these species. It is found that sulfur adsorbs on the face-centered cubic hollow site on Ni(111) with a S-Ni bond length of 2.20 +/- 0.02 Angstrom. The thiolate species formed at 150 K has the C-S bond tilted at similar to 35 degrees to the surface normal with a C-S bond length of 1.85 +/- 0.02. Angstrom and a S-Ni bond length similar to that for adsorbed sulfur (2.2 Angstrom). The methyl group is tilted toward the bridge site and the thiolate appears to be adsorbed on the face-centered cubic site although there may also be adsorption in the hexagonal close packed site. The species formed at 250 K adsorbs on a reconstructed surface where the chemical shift of the S 2p core level indicates that it adsorbs at a four-fold site and the angle-resolved XPS data indicate that the C-S bond is oriented normal to the surface. The calculated angular variations in intensity are consistent with this interpretation but cannot distinguish between the various models proposed for the reconstructed surface. (C) 1997 Elsevier Science B.V.