Using a combination of time-lapse high-resolution scanning tunnelling microscopy

and density functional theory calculations, the formation and diffusion of water

dimers on hydrated rutile TiO2(110)-(1x1) surfaces was revealed. That is, on

surfaces containing OHbr groups. 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. A hydrogen bond-mediated rollover mechanism

for the water dimers was suggested to explain the experimental findings.

Formation and Diffusion of Water Dimers on Rutile TiO2(110). J.Matthiesen,

J.Ø.Hansen, S.Wendt, E.Lira, R.Schaub, E.Lægsgaard, F.Besenbacher, B.Hammer:

Physical Review Letters, 2009, 102[22], 226101