The photochemistry of oxygen adsorbed on TiO 2 (110) at 30 K and annealed up to 600 K is investigated. UV irradiation results in exchange of atoms between chemisorbed and physisorbed oxygen. Annealing chemisorbed oxygen to 350 K maximizes these exchange reactions, while such reactions are not observed for oxygen that is dissociatively adsorbed on TiO 2 (110) at 300 K. For oxygen annealed to 350 K, the exchange products photodesorb in the plane perpendicular to the bridge-bonded oxygen rows at an angle of 45°. In contrast, chemisorbed O 2 photodesorbs normal to the surface. Remarkably, the chemisorbed species is stable under multiple cycles of UV irradiation. Atoms in the chemisorbed species can be changed from 18 O to 16 O and then back to 18 O via the exchange reactions. The results show that annealing oxygen on TiO 2 (110) to ∼350 K produces a stable chemical species with novel photochemical properties. Possible forms for the photoactive species include O 2 adsorbed in a bridging oxygen vacancy or tetraoxygen.
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Petrik et al. (2011) studied this question.
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