Gas-Phase Chemistry of Bare V+ Cation with Oxygen and Water at Room Temperature: Formation and Hydration of Vanadium Oxide Cations

Mass spectrometric experiments at extremely low (<10 -6 mbar) and moderate (0.5 mbar) pressures are used to examine the reactions of atomic vanadium cation with molecular oxygen and water. With O 2, rapid O-atom abstraction gives rise to the formation of VO + cation ( k = 3 × 10 -10 cm 3 molecule -1 s -1 ). Interestingly, despite a similar thermochemistry, the O-atom transfer from water to bare V + is less efficient by more than an order of magnitude ( k = 8 × 10 -12 cm 3 molecule -1 s -1 ). Subsequent associations of VO + with either O 2 or H 2 O occur with very low efficiencies and involve termolecular stabilization mechanisms. The low probability of degenerate 16 O/ 18 O exchange between VO + and water indicates the operation of a sizable kinetic barrier. Ab initio calculations using density functional theory lend further support to the interpretation of the experimental data and provide the first thermochemical information on VO n + cations with n > 2, as well as some hydrated species. In general, the dipolar water ligand is found to be much more strongly bound to the cationic vanadium complexes than is dioxygen.