The adsorption site and orientation of CH 3S on Ni(111)

Abstract

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(111) 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 A ̊ . The thiolate species formed at 150 K has the CS bond tilted at ∼35° to the surface normal with a CS bond length of 1.85±0.02 A ̊ and a SNi bond length similar to that for adsorbed sulfur (2.2 Å). 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.