Matrix studies of the thermal and photolytic reactions of Ga vapour species with H2O: formation and characterisation of the adducts Ga·OH2 and Ga2·OH2 and the photoproducts HGaOH, GaOH and Ga(μ-H)(μ-OH)Ga

Abstract

IR and UV–vis spectra have been used to chart the thermal and photolytic reactions occurring during or after the codeposition of Ga vapour with an excess of H₂O-doped Ar. Following the formation of the loosely bound adducts Ga⋯OH₂ and Ga₂⋯OH₂, detected after deposition of the matrix, UV irradiation (200 ≤ λ ≤ 400 nm) causes Ga⋯OH₂ to rearrange with insertion of the metal atom into an O–H bond forming the Ga(II) hydride HGaOH, while visible irradiation (λ = ca. 580 nm) causes Ga₂⋯OH₂ to rearrange with the formation of cyclic Ga(μ-H)(μ-OH)Ga. Broad-band photolysis (200 ≤ λ ≤ 800 nm) results in the destruction of both these products, with HGaOH decaying to GaOH. Characterisation of the various molecules by IR spectroscopy has been underpinned by reference (i) to the effects of isotopic change (^1,2H, ^16,18O and ^69,71Ga) and (ii) to the results of density functional theory (DFT) calculations. The properties of the molecules are compared with those of related species, and the mechanisms of the photochemical changes are discussed.