A previous report, in which scanning tunnelling microscopy had shown that adsorbed molecular oxygen locally induced anisotropic surface vacancy diffusion by dissociation near the vacancy, was inconsistent with negative observations of isotopic mixing between adsorbed 18O2 and the 16O atoms in the TiO2 lattice. Using adsorbed 18O2 on TiO2(110), prepared identically to the surface studied by STM, both the photodesorption and thermal desorption of adsorbed O2 fail to detect any isotopic exchange with lattice O. These results suggested that the mechanism proposed for the O2-mediated vacancy diffusion had to be modified.

Molecular Oxygen-Mediated Vacancy Diffusion on TiO2(110) - New Studies of the Proposed Mechanism. Thompson, T.L., Diwald, O., Yates, J.T.: Chemical Physics Letters, 2004, 393[1-3], 28-30