SYMMETRY CONTROLLED SURFACE PHOTOCHEMISTRY OF METHANE ON PT(111)

Adsorbed states of methane on Pt(111) and subsequent processes photoin duced by ArF laser irradiation (193 nm) have been studied by infrared reflection absorption spectroscopy. Adsorption degrades the symmetry o f first layer methane from T-d to C-3v but the overlayer methane keeps T-d. Only the C-3v CH4 in the first layer is photodissociated into CH 3 and H species. These reaction products modify the surface in such a way as to make the remaining CH4 molecules photochemically inactive, a nd thus the reaction becomes self-limiting. The lifted degeneracy cont rols the surface photochemistry.