Radiation chemistry of aqueous solutions of hydrazine Part 3. The chain reaction in oxygenated solutions irradiated with 60Co γ-rays

Abstract

The radiation-induced decomposition by 60Co γ-rays of oxygen saturated aqueous solutions of hydrazine has been measured over the pH range 3.5 to 11.7. A reaction set has been devised which accounts for the experimental observations based on decomposition proceeding by a pH-dependent chain reaction propagated by hydrazil radicals (specifically N2H3) reacting with O2 and the resulting HO2/O2- radicals oxidising hydrazine (N2H5+/N2H4) to hydrazil radicals (N2H4+/N2H3). Chain termination is via the self-reactions of HO2-/O2-. The pH dependence of the chain length is consistent with (a) HO2/O2- having different reactivity towards N2H4/N2H5+ in the propagating step, and (b) the known pH dependence of the termination reaction. The values of the rate constants of the propagation reactions that simulate the experimental data quite well are (in units of d mol-1 s-1): k(HO2+N2H5+)=10; k(HO2+N2H4)=70; k(O2-+N2H5+)=100; k(O2-+N2H4)=2.2; each with an estimated uncertainty of ±10%. There is no evidence that N2H4+ is a chain carrier.