Electron- and Hole-Mediated Reactions in UV-Irradiated O2 Adsorbed on Reduced Rutile TiO2(110)

Abstract

The ultraviolet (UV) photon-stimulated reactions in oxygen adsorbed on reduced TiO2(110) at low temperatures (<100 K) are studied. When a single O2 is chemisorbed in each bridging oxygen vacancy, only ∼14% of the O2 desorbs after prolonged UV irradiation. For the remaining O2 on the surface after irradiation, about one-half dissociates, and the other one-half is left in a nondissociated state that is inactive for hole-mediated photodesorption. For the maximum coverage of chemisorbed oxygen, the fraction of O2 that photodesorbs increases substantially, but is still only ∼40%. However, when physisorbed oxygen is also present, ∼70% of the initially chemisorbed O2 photodesorbs. On the basis of the experimental results, we propose that both hole- and electron-mediated reactions with O2 chemisorbed on TiO2(110) are important. Hole-mediated reactions lead to O2 photodesorption, while electron-mediated reactions lead to O2 dissociation. The electron-mediated reactions explain the low total photodesorption yield w...