The photochemistry of CH4 adsorbed on Pt(111) studied by high resolution fast XPS

The photochemistry induced at 40 K by synchrotron radiation at 400 eV in CH 4 molecules adsorbed on Pt(1 1 1) was studied by high resolution fast XPS. The photoreactions were monitored by acquiring the C1s core level spectrum as a function of time for methane adlayers with coverage ranging from submo nolayer to multilayer regime. We have observed molecular desorption of the multilayer and effective dissociation in the layer in contact with the meta l. Differently from UV photons and low energy e-beam. induced dissociation of CH4 adsorbed on Pt(1 1 1) - which only produced adsorbed CH3 and H fragm ents - the C1s core level measured on methane photodissociated at 400 eV sh ows that other species are formed, which start to thermally dissociate at a bout 100 K, producing CH and possibly H. Probable candidates are CH2, forme d by multiple C-H bond cleavage together with CH., groups during the initia l methane photodissociation, or a C-C containing intermediate, resulting fr om methyl surface chemistry. (C) 2001 Elsevier Science B.V. All rights rese rved.