A combination of high-resolution scanning tunneling microscopy and density functional theory is utilized to study the interaction of water with the reduced ${\mathrm{TiO}}_2(110)\mathrm{\text{−}}(1\times 1)$ surface. As the direct product of water dissociation in oxygen vacancies, paired hydroxyl groups are formed. These pairs are immobile and stable unless they interact with adsorbed water molecules. As a result of these interactions, protons are transferred to adjacent oxygen rows, thereby forming single hydroxyl groups. Additionally, we show that hydroxyl groups facilitate the diffusion of water molecules over the oxygen rows.

• Received 16 September 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.066107