Experimental evidence for mixed dissociative and molecular adsorption of water on a rutile TiO2(110) surface without oxygen vacancies

We present evidence for mixed molecular and dissociative water adsorption at monolayer coverage on a rutile TiO₂(110) surface free from oxygen vacancies using synchrotron radiation photoemission. At monolayer coverage the OH:H₂O ratio is close to 0.5 and reducing the coverage by heating yields an increased OH:H₂O ratio. At room temperature neither species originating from the monolayer on the defect-free surface can be detected. The OH species of the monolayer hence recombines and leaves the surface at much lower temperatures than OH formed by water dissociation on oxygen vacancies.