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.