CHARACTERISTIC VIBRATIONAL MODES OF H2O ADSORBED MOLECULARLY AND DISSOCIATIVELY ON TITANIUM OXIDE CLUSTERS.

To provide useful information on dissociation of water molecule on (TiO2)n clusters for experimental verification, we have calculated the infrared (IR) and Raman spectra of three possible states involved, namely molecularly adsorbed state, metastable state and dissociatively adsorbed state, using density functional theory at the B3LYP/6-311G(d) level. We find that the characteristic bands of H2O molecules below 2000 cm-1 in both IR and Raman spectra vanish upon both molecular and dissociative adsorption of H2O. In the high frequency range of 3600-4200 cm-1, the adsorption caused the single IR peak of water to split into two bands, while the dissociation removed the one at lower frequency and blue shifted slightly the higher frequency band. The two Raman peaks of the water molecule in the same high frequency range were slightly blue shifted upon adsorption but the one at lower frequency was removed upon dissociation, while the one at high frequency blue shifted slightly. The intensities of vibrational modes of water in 3600-4200 cm-1 are generally significantly enhanced upon both molecular and dissociative adsorption. Our results show clearly signatures of dissociation of water molecule into hydroxyl radical at the terminal site. [ABSTRACT FROM AUTHOR]