Electronic structure of titanium oxide clusters: TiOy (y = 1−3) and (TiO2)n (n = 1−4)

The electronic structure of two series of small titanium oxide clusters, ${\mathrm{TiO}}_y$ $\text{(y\hspace{0.17em}=\hspace{0.17em}1−3)}$ and $({\mathrm{TiO}}_2{)}_n$ $\text{(n\hspace{0.17em}=\hspace{0.17em}1−4),}$ is studied using anion photoelectron spectroscopy. Vibrationally resolved spectra are obtained for ${\mathrm{TiO}}^{-}$ and ${\mathrm{TiO}}_2^{-}.$ Six low‐lying electronic states for TiO are observed with five of these excited states resulting from multielectron transitions in the photodetachment processes. ${\mathrm{TiO}}_2$ 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 ${\mathrm{TiO}}_2$ are observed with excitation energies at 1.96 and 2.4 eV, respectively. ${\mathrm{TiO}}_3$ 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 ${\mathrm{TiO}}_2,$ respectively. The larger $({\mathrm{TiO}}_2{)}_n$ clusters are all closed‐shell with HOMO‐LUMO gaps similar to that of ${\mathrm{TiO}}_2$ and with increasing EAs: 2.1 eV for $\text{n\hspace{0.17em}=\hspace{0.17em}2,}$ 2.9 eV for $\text{n\hspace{0.17em}=\hspace{0.17em}3,}$ 3.3 eV for $\text{n\hspace{0.17em}=\hspace{0.17em}4.}$ The small HOMO‐LUMO gaps for the clusters compared to that of bulk ${\mathrm{TiO}}_2$ are discussed in terms of the structure and bonding of these clusters.