Adsorption and reactions of methanethiol on clean and modified Ni(110)

The reactions of methanethiol on clean and modified Ni(110) have been studied under ultrahigh-vacuum conditions by temperature-programmed reactions (TPR), including deuterium incorporation studies. Surface bound molecular fragments were identified by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS). The TPR data indicate that the major products of the reactions of methanethiol with clean Ni(110) surfaces are methane and hydrogen. Methane desorbs in a reaction-limited peak at 276 K, which does not shift with methanethiol exposure. Hydrogen desorption occurs in several peaks depending on the exposure. The coverage dependence of the methane yield indicates a competition between decomposition and reaction to form methane. At low coverages, decomposition is the major pathway while at higher coverages methane formation dominates. Vibrational spectroscopy (HREELS) indicates the presence of the methyl thiolate intermediate at temperatures less than 200 K. X-ray photoelectron spectroscopy and deuterium incorporation experiments confirm this assignment. A mechanism has been proposed based on hydrogenolysis of the methyl thiolate species and is consistent with all of the data. The appropriate rate equations associated with this mechanism have been solved numerically to predict the TPR data, and qualitative agreement was achieved. Methanethiol reacts with sulfur- and oxygen-modified Ni(110) surfaces to produce methane, hydrogen, and, in the case of the oxidized surfaces, water. The major effect of the modifier was to enhance the formation of methane relative to decomposition. These observations can be explained by either electronic or structural effects.