Photoemission studies of H 2S, H 2 and S adsorbed on Ru(110): Evidence for an adsorbed SH species

Abstract

H 2S, H 2 and S adsorbed on Ru(110) have been studied by angle-integrated ultraviolet photoemission (UPS) as part of a study of the effect of adsorbed sulfur, a common catalytic poison, on this Ru surface. For low exposures of H 2S at 80 K, the work function rises to a value 0.16 eV above that of clean Ru(110) while the associated UPS spectra ( hν = 21.2 eV) exhibit features similar to those of H(ads) and S(ads) and different from those of molecular H 2S. We conclude that H 2S dissociates completely at low coverages on Ru(110) at 80 K. At intermediate exposures the work function drops and the UPS spectra show new features which are attributed to the presence of an adsorbed SH species. This appears to be the first direct observation of this surface complex. At higher exposures the work function saturates at a value 0.36 eV below the clean value; the UPS spectra change markedly and indicate the adsorption of molecular H 2S. Heating adsorbed H 2S leaves a stable layer of S(ads) on Ru(110). The surface with adsorbed sulfur strongly modifies the adsorption at 80 K of a number of molecules relative to the clean Ru(110) surface.