Figure 1. 2PP spectra of the a) stoichiometric and b) reduced TiO2 surfaces before and after deposition of ~1 ML of H2O. The H2O/TiO2 spectra are taken with s- and p-polarized light. The difference between thus normalized p- and s-polarized spectra (green) for the reduced surface isolates the additional density of states attributed to the water-induced resonance. The inset shows an oxygen vacancy defect in bridging oxygen rows, which is the site of H2O dissociation.