BIMOLECULAR SURFACE PHOTOCHEMISTRY - MECHANISMS OF CO OXIDATION ON PT(111) AT 85-K

Results from a photoinduced bimolecular surface reaction are presented. The reaction, occurring from CO coadsorbed with O2 on Pt(111) at 85 K, is O2 + CO + hv --> O + CO2. Surface analysis techniques employed include electron energy loss spectroscopy (EELS), thermal desorption spectroscopy (TDS), photon-induced desorption spectroscopy (PID), and low energy electron diffraction (LEED). The incident power, photon energy, and polarization dependences of the photochemical processes, O2 photodesorption and CO2 photoproduction, were characterized, with the cross section for both processes being 3 x 10(-19) cm2 at 240 nm. Electronic EELS studies were performed to acquire information on the electronic structure of O2 on Pt(111). The experimental results are compared to predictions of models describing direct dipole excitation of the O2-Pt system and substrate mediated hot carrier mechanisms. Reaction mechanisms involving photogenerated hot O atoms or excited O2 molecules on the surface are considered. The implications of this work on surface reaction dynamics are discussed.