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

The radiation-induced decomposition by Co-60 gamma-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 o bservations based on decomposition proceeding by a pH-dependent chain react ion propagated by hydrazil radicals (specifically N2H3.) reacting with O-2 and the resulting HO2./O-2(.-) radicals oxidising hydrazine (N2H5+/N2H4) to hydrazil radicals (N2H4.+/N2H3.). Chain termination is via the self-reacti ons of HO2.-/O-2(.-). The pH dependence of the chain length is consistent w ith (a) HO2./O-2(.-) having different reactivity towards N2H4/N2H5+ in the propagating step, and (b) the known pH dependence of the termination reacti on. The values of the rate constants of the propagation reactions that simu late the experimental data quite well are (in units of d mol(-1) s(-1)): k( HO2 + N2H5+) = 10; k(HO2. + N2H4) = 70; k(O-2(.-) + N2H5+) = 100; k(O-2(.-) + N2H4) = 2.2; each with an estimated uncertainty of +/- 10%. There is no evidence that N2H4.+ is a chain carrier.