Photodesorption and trapping of molecular oxygen at the TiO2(110)-water ice interface

By means of temperature programmed desorption (TPD), static secondary ion mass spectroscopy (SSIMS), and electron energy loss spectroscopy (EELS), we have investigated further the states of oxygen adsorbed on rutile TiO2. Previous work has shown that annealing the (110) surface in a vacuum produces isolated bridging oxygen vacancies, and that these vacancies are intimately connected with molecular and dissociative oxygen adsorption channels. We find that at 115 K illumination of the oxygen-exposed surface with 4.1 eV photons results in photodesorption of the oxygen associated with a TPD state centered on 410 K, in contrast to the remaining oxygen destined for a dissociative channel. An unusual effect of water overlayers on the photochemical properties of the O/TiO2(110) system is explored. For thick overlayers, it is possible to generate via UV irradiation a previously unobserved oxygen TPD state. Evidence is presented for this new Oz TPD state originating from the photolysis of an O-2-water adduct.