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 sand p-polarized light with the plane of incidence parallel to the [001] and [1(1) over bar 0] 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.