Competing water dissociation channels on rutile TiO2(110)

The interplay between two different water dissociation channels on rutile TiO₂(110) was studied with the use of synchrotron radiation photoelectron spectroscopy. It was found that water dissociation at oxygen vacancies competes with water dissociation on defect-free regions such that one vacancy assisted dissociation event cancels one dissociation event on defect-free regions. The quenching affects the thermally most stable dissociated species that form at low coverage on the defect free surface but does not affect the stability of molecular water. As a result, molecular adsorption becomes favored at low coverage on a surface where all vacancies have been hydroxylated. The presence of competitive dissociation channels rationalizes the difficulties in identifying dissociated species on defect-free regions in previous studies.