DETECTION OF CHEMISORBED METHYL AND METHYLENE GROUPS - SURFACE-CHEMISTRY OF METHYL-IODIDE ON PT(111)

The thermal chemistry of methyl iodide on Pt(111) surfaces was studied by using thermal programmed desorption (TPD), X-ray photoelectron (XPS), and reflection-absorption (RAIRS) spectroscopies. Spectra obtained at low temperatures for both normal and fully deuterated methyl iodide indicate that chemisorption is molecular and that the adsorption geometry changes with coverage, starting with a tilted configuration after small doses and switching to a structure where the C-I bond is perpendicular to the surface above half-saturation. The only reaction that can be thermally activated at low coverages is a C-I bond breaking step, which is then followed by total dehydrogenation and by hydrogen desorption. At higher coverages, however, an appreciable amount of methane also desorbs, and both methyl and methylene groups form on the surface.