On the mechanism of the γ-radiolysis of deoxygenated aqueous solutions of hydrazine

Abstract

A reaction mechanism has been devised by trial and error that accounts for most of the data that have been obtained from γ-radiolysis studies under deaerated conditions and which hitherto have not been satisfactorily explained. The major features of the proposed mechanism are the following. (a) Hydrazyl radicals N₂H₄^•+ and ^•N₂H₃ react by disproportionation to form N₂H₂ and hydrazine, and by combination either as the free radicals or with one of them complexed with a hydrazine molecule, N₂H₅⁺ or N₂H₄, to produce N₂ + 2NH₃. This accounts for the observed strong dependence of the radiolytic decomposition yields (G-values) on [N₂H₅⁺]. (b) Hydrogen atoms (hydrated electrons) are proposed to react with N₂H₅⁺ (N₂H₄) by a split path to form H₂ + N₂H₄^•+ (^•N₂H₃) and ^•NH₂ + NH₄⁺ (NH₃), which helps to account for the observed values of G(H₂); reduction of N₂H₂ by H^• to ^•N₂H₃ is also required to explain fully the values of G(H₂). (c) In alkaline solution the decrease in decomposition yields is explained in terms of the dissociation of H₂O₂ to HO₂⁻, which is more readily oxidised to O₂^•−. This, together with the much longer lifetime of O₂^•− at high pH, results in the reduction by O₂^•− of ^•N₂H₃ back to N₂H₄. The effect of added H₂O₂ in acidic solution can be explained if it forms a complex with N₂H₄^•+ followed by reaction with another N₂H₄^•+ to form N₂ + 2H₂O.