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 i nclude electron energy loss spectroscopy (EELS), thermal desorption sp ectroscopy (TDS), photon-induced desorption spectroscopy (PID), and lo w energy electron diffraction (LEED). The incident power, photon energ y, and polarization dependences of the photochemical processes, O2 pho todesorption and CO2 photoproduction, were characterized, with the cro ss section for both processes being 3 x 10(-19) cm2 at 240 nm. Electro nic EELS studies were performed to acquire information on the electron ic structure of O2 on Pt(111). The experimental results are compared t o predictions of models describing direct dipole excitation of the O2- Pt system and substrate mediated hot carrier mechanisms. Reaction mech anisms 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.