ON ORIGIN OF PRIMARY HYDROGEN PEROXIDE YIELD IN GAMMA RADIOLYSIS OF WATER

In an attempt to throw light on the origin of GH2O2, hydrogen peroxide yields were determined in deaerated aqueous solutions (pH 1.3-13) of different substances, irradiated with 60Co γ-rays. Only those systems for which the reaction mechanism enables the direct measurement of GH2O2 were chosen: 1-propanol, ethanol, acrylamide, acetone, and potassium nitrate. Particular care was taken to ensure that the values derived represent the initial yields. It was shown that homogeneous kinetics can be used to express the dependence of GH2O2 on hydroxyl radical scavenger concentration, and the origin of intraspur H2O2 in a pseudo-first-order process was considered. However, all experimental data obtained in this work demonstrate that GH2O2 values depend on the reactivities as required in the diffusion kinetic model; the fractional lowering of primary peroxide yield decreases with increasing reactivity of the OH scavenger and increases with increasing eaq- scavenger reactivity. Theoretical kinetic curves calculated by Kuppermann and by Mozumder and Magee, using the same parameters which furnish good agreement with LET effects, satisfy reasonably well the results presented here, hence the conclusion that the origin of GH2O2 lies in the recombination of OH radicals within the spur. The experimental results also enable the determination of the primary hydrogen peroxide yields from the γ radiolysis of water: 0.76 ± 0.01 and 0.67 ± 0.01 at pH 1.3 and about 6, respectively. At pH 13 acrylamide solutions give 0.56 < GH2O2 < 0.67 and other studies are desirable before a definite conclusion is made.