Infrared Spectroscopy of Solvation in the TaO2+ Hydrolysis Reaction.

Abstract

The solvent effect of the TaO2+ reaction with water molecules in the gas phase is examined. Stoichiometric TaO2(H2O)n+ 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)n+ 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.