Tetraoxygen on reduced TiO2(110): oxygen adsorption and reactions with bridging oxygen vacancies.

Oxygen adsorption on reduced TiO2(110) is investigated using temperature programmed desorption and electron-stimulated desorption. At low temperatures, 2 O(2) molecules can be chemisorbed in each oxygen vacancy. These molecules do not desorb upon annealing to 700 K. Instead, for 200 K<T<400 K, the 2 O(2) convert to another species, which has four oxygen atoms, i.e., tetraoxygen, that decomposes at higher temperatures. In contrast, when only 1 O(2) is adsorbed in an oxygen vacancy, the molecule dissociates upon annealing above ~150 K to heal the vacancy in agreement with previous results.