Oxygen adsorption on reduced ${\mathrm{TiO}}_2(110)$ is investigated using temperature programed desorption and electron-stimulated desorption. At low temperatures, 2 ${\mathrm{O}}_2$ molecules can be chemisorbed in each oxygen vacancy. These molecules do not desorb upon annealing to 700 K. Instead, for $200\mathrm{K}<T<400\mathrm{K}$, the 2 ${\mathrm{O}}_2$ convert to another species, which has four oxygen atoms, i.e., tetraoxygen, that decomposes at higher temperatures. In contrast, when only 1 ${\mathrm{O}}_2$ is adsorbed in an oxygen vacancy, the molecule dissociates upon annealing above $\sim 150\mathrm{K}$ to heal the vacancy in agreement with previous results.

• Received 11 January 2008

DOI:https://doi.org/10.1103/PhysRevLett.100.196102