Electronic structure of titanium oxide clusters: TiOy „y51 – 3... and „TiO2...n „n51 – 4..

The electronic structure of two series of small titanium oxide clusters, TiOy (y51 – 3) and (TiO2)n (n51 – 4), is studied using anion photoelectron spectroscopy. Vibrationally resolved spectra are obtained for TiO and TiO2 . Six low-lying electronic states for TiO are observed with five of these excited states resulting from multielectron transitions in the photodetachment processes. TiO2 is found to be closed-shell with a 2 eV highest occupied molecular orbital/lowest unoccupied molecular orbital ~HOMO-LUMO! gap. The two lowest triplet and singlet excited states of TiO2 are observed with excitation energies at 1.96 and 2.4 eV, respectively. TiO3 is found to have a very high electron affinity ~EA! of 4.2 eV, compared to 1.30 and 1.59 eV for TiO and TiO2, respectively. The larger (TiO2)n clusters are all closed-shell with HOMO-LUMO gaps similar to that of TiO2 and with increasing EAs: 2.1 eV for n52, 2.9 eV for n53, 3.3 eV for n54. The small HOMO-LUMO gaps for the clusters compared to that of bulk TiO2 are discussed in terms of the structure and bonding of these clusters. © 1997 American Institute of Physics. @S0021-9606~97!02444-6#