Symmetry Controlled Surface Photochemistry of Methane on Pt(111)

Abstract

Adsorbed states of methane on Pt(111) and subsequent processes photoinduced by ArF laser irradiation (193 nm) have been studied by infrared reflection absorption spectroscopy. Adsorption degrades the symmetry of first layer methane from $T_d$ to $C_{3v}$, but the overlayer methane keeps $T_d$. Only the $C_{3v}$ C${\mathrm{H}}_4$ in the first layer is photodissociated into C${\mathrm{H}}_3$ and H species. These reaction products modify the surface in such a way as to make the remaining C${\mathrm{H}}_4$ molecules photochemically inactive, and thus the reaction becomes self-limiting. The lifted degeneracy controls the surface photochemistry.