Infrared Spectroscopy of Solvation in the TaO Hydrolysis Reaction.

The solvent effect of the TaO reaction with water molecules in the gas phase is examined. Stoichiometric TaO(HO) cations are generated by the laser vaporization of a tantalum metal target in the pulsed supersonic expansion of HO/He mixed gas. The infrared photodissociation spectra of TaO(HO) cations are measured using the argon-tagging technology in the 2800-3850 cm region. Density functional theory calculations are carried out to identify the observed infrared bands and elucidate the reaction mechanism. In the TaO reaction with one HO molecule, both the hydrated adduct HO-TaO and dihydroxide TaO(OH) are generated. The coexistence of tetrahydroxide Ta(OH) and hydrated dihydroxide HO-TaO(OH) is seen when the second HO molecule is involved. However, only the hydrated HO-Ta(OH) product is obtained in the TaO reaction with three HO 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.