The adsorption site and orientation of CH3S and sulfur on Ni(001) using angle-resolved X-ray photoelectron spectroscopy

Photoelectron diffraction from the S 2p core level has been used to determine the adsorption site and orientation of sulfur and methyl thiolate (CH3S) on Ni(001) by comparing the experimental data with the results of multiple scattering calculations. The theory was initially checked for atomic S, which is known to adsorb in the four-fold hollow site on Ni(001), and the results corresponded to the correct geometry. Comparison of calculated spectra with the experimental data indicates that chemisorbed atomic sulfur is located at 1.30___0.01 A above the first layer of nickel atoms on the (001) plane. At 100 K, CH3S adsorbs in the fourfold site on Ni(001), where the C-S bond is proposed to be oriented along the surface normal on Ni(001). A comparison between calculated and experimental results demonstrate that the C-S bond in adsorbed methyl thiolate is oriented perpendicular to the surface and is 1.85-t-0.1 _A long.