CHARGE SCAVENGING AND ENERGY TRANSFER IN GAMMA RADIOLYSIS OF BENZENE SOLUTIONS

The γ radiolysis of benzene solutions of N2O was studied over the concentration range 5-400 mM. Values of G(N2) are fitted with a published empirical equation for electron scavenging by N2O in cyclohexane. The equation corresponds to a model which involves (1) electron capture by N2O and (2) reaction of an anion produced via reaction 1 with another molecule of N2O; both reactions compete with charge neutralization. Each occurrence of reaction 1 not followed by reaction 2 yields one molecule of N2; each occurrence of reaction 1 followed by reaction 2 yields two molecules of N2. Reaction 1 is characterized by a parameter α which is proportional to the specific rate (ks) of the reaction and to an effective decay time (τ) for the distribution of geminate cation-electron separations produced in the solvent. For reaction 2, a parameter β is the analog of α. For G(geminate ions) = 3.9, best fit to the data is obtained for G(free ions) = 0, α in the range 0.65-0.75 M-1, and corresponding values of β in the range 32-15 M-1. Such a low value of α, as compared to α = 16 M-1 in cyclohexane, is interpreted in terms of an effect of solvent on ks and τ. Suppression of G(N2) is observed with c-C4F8, CH3Br, or trans-stilbene present in the N2O-C6H6 solutions. In turn, N2O suppresses the radiation-induced isomerization of trans-stilbene in benzene; analysis of the effect by use of α = 0.70 M-1 gives an estimate of direct and ionic contributions to benzene excitation in γ radiolysis as G = 2.0 and G = 3.4, respectively.