Infrared photodissociation spectroscopic investigation on VO+ and NbO+ hydrolysis catalyzed by water molecules

Abstract

We investigate the hydrolysis of vanadium/niobium monoxide cation (VO⁺/NbO⁺) with water molecules in the gas phase. Cationic argon-tagged intermediates, TMO(H₂O)_nAr_m⁺ (TM = V, Nb; n = 1–2, m = 1–2), are prepared for examination using infrared photodissociation spectroscopy. The structures of the intermediates are elucidated by comparing them with simulated spectra. VO(H₂O)Ar⁺ or NbO(H₂O)Ar⁺ (for n = 1) is intrinsically a hydrated adduct, represented by H₂O–VOAr⁺ or H₂O–NbOAr⁺, rather than a dihydroxide, V(OH)₂Ar⁺ or Nb(OH)₂Ar⁺. However, when a second H₂O molecule is involved (for n = 2), the dihydroxide V(OH)₂(H₂O)Ar⁺ and trihydroxide HNb(OH)₃Ar⁺ are formed. In this process, the six-member cyclic transition state formed by two H₂O molecules markedly reduces the hydrogen transfer energy barrier based on our calculations. This work provides more precise experimental evidence for the Grotthuss-like mechanism proposed in the studies of hydrolysis and tautomerization reactions.