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 de termine the adsorption site and orientation of sulfur and methyl thiol ate (CH3S) on Ni(001) by comparing the experimental data with the resu lts of multiple scattering calculations. The theory was initially chec ked for atomic S, which is known to adsorb in the four-fold hollow sit e on Ni(001), and the results corresponded to the correct geometry. Co mparison of calculated spectra with the experimental data indicates th at chemisorbed atomic sulfur is located at 1.30 +/- 0.01 Angstrom abov e the first layer of nickel atoms on the (001) plane. At 100 K, CH3S a dsorbs in the four-fold site on Ni(001), where the C-S bond is propose d to be oriented along the surface normal on Ni(001). A comparison bet ween calculated and experimental results demonstrate that the C-S bond in adsorbed methyl thiolate is oriented perpendicular to the surface and is 1.85 +/- 0.1 Angstrom long.