Applications of Sxps for Studying Surface Structure, Reaction Mechanisms and Kinetics

Abstract

REACTION MECHANISMS AND KINETICS 7 ) . a s U b m n s d -~-by a antnaQ d um us. ~u d a c m m n N a M -.\~-84oR214M). -. us.G o M m n a n r s P r r . ABSTRACTSoft x-ray photoelectron spectroscopy ( S X P S ) from the S 2p core level has been used to study adsorbate induced reconstruction, identify reaction intermediates and study reaction kinetics on the Ni( 11 1) surface. The S 2p binding energy is affected by the nature of the surface adsorption site. It has been determined from the number of S 2p states and their relative binding energies that adsorbed S induces a reconstruction of the Ni ( 1 1 1 ) surface and that the S adsorbs in fourfold sites on terraces and in troughs. S 2p SXPS has also been used to identify adsorbed species during the thermal decomposition of methanethiol on Ni(l11). CH,SH adsorbs as CH,S-at low temperatures. Above 200 K, the CH,S-changes adsorption site and the C-S bond begins to cleave. The relative concentrations of CH,S-in the two different sites and of atomic S have been monitored as a function of temperature and initial coverage. As a result of the sensitivity and resolution available in SXPS, reactions rates and kinetic parameters have been obtained for the decomposition of benzenethiol on Ni(ll1) by monitoring the changes in the surface composition continuously as a function of temperature and time.