Radiation chemistry of xenon trioxide, xenate and perxenate, and photochemistry of perxenate. A pulse radiolysis and laser flash photolysis study

Abstract

Unstable species containing xenon in the formal oxidation states five, Xe^V, and seven, Xe^VII, were observed by pulse radiolysis of aqueous solutions of xenon trioxide, XeO₃, at pH 8–9 and of xenate, HXeO^–₄, at pH 11–13. Xe^VII and species containing xenon in the formal oxidation state nine, Xe^IX, were observed in pulse radiolysis and flash photolysis of aqueous solutions of perxenate, HXeO^3–₆, at pH 11–13. The formulae HXeO₃ and H₃XeO^2–₇ are assumed for Xe^V and Xe^IX, whereas the observations suggest that Xe^VII corresponds to three different species for which the formulae HXeO₄, HXeO^2–₅ and H₃XeO^2–₆ are assumed. HXeO₃ and H₃XeO^2–₆ are formed in reactions of the hydrated electron with XeO₃ and HXeO^3–₆, respectively. HXeO₄ and H₃XeO^2–₇ are formed in reactions of the hydroxyl radical with XeO₃ and HXeO^3–₆ in which the hydroxyl radical adds to a ligand oxygen atom to form peroxy compounds. HXeO^2–₅ is formed in a reaction with the hydroxyl radical anion in which the hydroxyl radical anion adds to the xenon atom and by photolysis of HXeO^3–₆: HXeO^3–₆ [graphic omitted] HXeO^2–₅+ O^–. Xe^V, Xe^VII and Xe^IX and corresponding iodine species in the oxidation states four, six and eight have similar spectra and kinetics of disappearance. Estimated values of standard Gibbs energy of formation of the xenon species are used for selecting thermodynamically feasible mechanisms for one-electron reduction of perxenate and for the decomposition of perxenate in acid solution.