Polarization- and Azimuth-Resolved Infrared Spectroscopy of Water on TiO2(110): Anisotropy and the Hydrogen-Bonding Network.

We have investigated the structure and dynamics of thin water films adsorbed on TiO2(110) using infrared reflection-absorption spectroscopy (IRAS) and ab initio molecular dynamics. Infrared spectra were obtained for s- and p-polarized light with the plane of incidence parallel to the [001] and [11̅0] azimuths for water coverages ≤ 4 monolayers. The spectra indicate strong anisotropy in the water films. The vibrational densities of states predicted by the ab initio simulations for 1 and 2 monolayer coverages agree well with the observations. The results provide new insight into the structure of water on TiO2(110) and resolve a long-standing puzzle regarding the hydrogen bonding between molecules in the first and second monolayers on this surface. The results also demonstrate the capabilities of polarization- and azimuth-resolved IRAS for investigating the structure and dynamics of adsorbates on dielectric substrates.