Hydrogen Bonds and Vibrations of Water on (110) Rutile

We study the relation between the hydrogen bonding and the vibrational frequency spectra of water on the (110) surface of rutile (α-TiO2) with three structural layers of adsorbed water. Using ab initio molecular dynamics simulations at 280, 300, and 320 K, we find strong, crystallographically controlled adsorption sites, in general agreement with synchrotron X-ray and classical molecular dynamics simulations. We demonstrate that these sites are produced by strong hydrogen bonds formed between the surface oxygen atoms and the sorbed water molecules. The strength of these bonds is manifested by substantial broadening of the stretching mode vibrational band. The overall vibrational spectrum obtained from our simulations is in good agreement with inelastic neutron scattering experiments. We correlate the vibrational spectrum with different bonds at the surface to transform these vibrational measurements into a spectroscopy of surface interactions.