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.