Electron scavenging in the radiolysis of supercritical propane and propylene: Effect of density

Abstract

The nitrogen yield observed upon electron scavenging by N₂O in the γ radiolysis of supercritical propane and propylene at 120°C and at various densities can be quantitatively described by the square root model, $\mathrm{G(}{\mathrm{N}}_2\mathrm{)=G(}{\mathrm{N}}_2{)}_{\mathrm{fi}}\mathrm{+G(}{\mathrm{N}}_2{)}_{\mathrm{gi}}\mathrm{(A[}{\mathrm{N}}_2\mathrm{O}{\mathrm{])}}^{\text{1/2}}$ , in the lower concentration range. G(N₂)_fi decreases smoothly with increase in density in both hydrocarbons. At a given density, G(N₂)_fi in propane is always larger than that in propylene, e.g., at d = 0.35 g/ml, G(N₂)_fi = 1.13 and 0.36, respectively. The analysis of G(N₂)_fi on the assumption G(N₂)_fi = G(free ion) indicates that (i) the density‐normalized range of electrons is constant over the density range of 0.24–0.42 g/ml in propane and 0.12–0.44 g/ml in propylene, and (ii) the efficiency of electron thermalization in propylene is about twice as good as in propane. The results are related to the thermalization mechanisms of electrons in hydrocarbons. An interpretation of the change in values of A with density is given in terms of the change in the distribution function of ion‐electron separation distances and the diffusion coefficient of electrons.