The Formation of [TiO(H₂O)_n]⁺ Cluster Ions

Gas phase [TiO(H₂O)_n]⁺ clusters are produced by laser induced plasma reactions of titanium and water, and studied using a triple quadrupole mass spectrometer. More than 60 water molecules cluster onto TiO⁺; but, no [Ti(H₂O)_n]⁺ clusters are observed. The cluster size distributions of [TiO(H₂O)_n]⁺ can be fit to log-normal curves Considered in the context of other data reported herein for cluster distributions of [NbO(H₂O)_n]⁺, it is concluded that the cluster formation and growth proceed via a coalescence mechanism between [TiO(H₂O)_n]⁺ and water molecule(s), which may lead to the formation of solvation shells. Ab initio calculations were employed to gain insight into the structures and energetics of small [TiO(H₂O)_n]⁺ clusters with n = 1-3. A charge donation from the water ligand to the TiO⁺ ion is found, which indicates the existence of high binding energies between water and TiO⁺. These experimental and theoretical results further contribute to an understanding of ion-induced nucleation in general, and hydration of TiO⁺, in particular.