Infrared Spectroscopy of Solvation in the TaO₂⁺ Hydrolysis Reaction

The solvent effect of the TaO₂⁺ reaction with water molecules in the gas phase is examined. Stoichiometric TaO₂(H₂O)⁺ cations are generated by the laser vaporization of a tantalum metal target in the pulsed supersonic expansion of H₂O/He mixed gas. The infrared photodissociation spectra of TaO₂(H₂O)⁺ cations are measured using the argon-tagging technology in the 2800-3850 cm^-1 region. Density functional theory calculations are carried out to identify the observed infrared bands and elucidate the reaction mechanism. In the TaO₂⁺ reaction with one H₂O molecule, both the hydrated adduct H₂O-TaO₂⁺ and dihydroxide TaO(OH)₂⁺ are generated. The coexistence of tetrahydroxide Ta(OH)₄⁺ and hydrated dihydroxide H₂O-TaO(OH)₂⁺ is seen when the second H₂O molecule is involved. However, only the hydrated H₂O-Ta(OH)₄⁺ product is obtained in the TaO₂ reaction with three H₂O molecules. Theoretical calculations indicate that in the reaction, the formation of a six-membered cyclic transition state through the hydrogen bond lowers the energy barrier significantly, which promotes the transfer of the hydrogen of hydrated adducts to generate di- and tetrahydroxides.