From the interplay of time-lapsed high resolution scanning tunnelling microscopy and density functional theory calculations, the formation and diffusion of water dimers on hydrated rutile TiO2(110)-(1x1) surfaces, i.e., surfaces containing OHbr groups, was revealed. At between ∼150 and ∼210K water monomers diffusing along the Ti troughs were found to form stable water dimers that diffused faster than the water monomers. An H bond mediated rollover mechanism operating for the water dimers explained the experimental findings.

Formation and Diffusion of Water Dimers on Rutile TiO2(110). Matthiesen, J., Hansen, J.O., Wendt, S., Lira, E., Schaub, R., Lægsgaard, E., Besenbacher, F., Hammer, B.: Physical Review Letters, 2009, 102[22], 226101