Stable compositions and geometrical structures of titanium oxide cluster cations and anions studied by ion mobility mass spectrometry

Geometrical structures of titanium oxide cluster cations and anions have been investigated by ion mobility mass spectrometry and quantum chemical calculations based on density functional theory. Stable cluster compositions with respect to collision induced dissociation were also determined by changing ion injection energy to an ion drift cell for mobility measurements. The Ti_nO_2n−1⁺ cations and Ti_nO_2n⁻ anions were predominantly observed at high injection energies, in addition to Ti_nO_2n⁺ for cations and Ti_nO_2n+1⁻ for anions. Collision cross sections of Ti_nO_2n⁺ and Ti_nO_2n+1⁻ for n = 1-7, determined by ion mobility mass spectrometry, were compared with those obtained theoretically as orientation-averaged cross sections for the optimized structures by quantum chemical calculations. All of the geometrical structures thus assigned have three-dimensional structures, which are in marked contrast with other oxides of late transition metals. One-oxygen atom dissociation processes from Ti_nO_2n⁺ and Ti_nO_2n+1⁻ by collisions were also explained by analysis of spin density distributions.