Final State Distributions of Methyl Photoproducts from the Photooxidation of Acetone on TiO2(110)

Abstract

The UV photooxidation of acetone on a reduced TiO2(110) surface was investigated using a combination of photodesorption and thermal desorption measurements and pump–probe laser detection of gas-phase products. In agreement with earlier studies, acetone adsorbed on TiO2 does not undergo a UV photoreaction unless codosed with molecular oxygen. The only gas-phase photoproducts are methyl radicals originating from fragmentation of the active acetone surface species and photodesorbed molecular oxygen. Postirradiation TPD measurements show that acetate is the primary surface product remaining after photooxidation. The dependence of the methyl radical formation rate on oxygen and thermal pretreatment of the TiO2 surface is consistent with the formation of an acetone–oxygen (diolate) complex involving adsorbed acetone and oxygen adatoms. Pump-delayed-probe laser techniques were used to measure the velocity and translational energy distributions of methyl radicals resulting from fragmentation of the acetone diolat...