Charge Separation and Similarities of Ionic Processes in the Radiolysis of Alkanes and of Water

Abstract

The charge‐pair separation distribution function, $$d\ln \mathrm{n\hspace{0.17em}/\hspace{0.17em}d}\ln \text{R\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}2.7}$$ is consistent with results from the rate of correlated ion‐pair recombination, as well as the temperature and field dependence of the electrical conductivity of n‐hexane under x irradiation for data reported by Allen et al. The $T$ dependence derives from (1) and $R_{\mathrm{escape}}{\mathrm{\hspace{0.17em}=\hspace{0.17em}e}}^2\mathrm{\hspace{0.17em}/\hspace{0.17em}\epsilon kT}$ . The combined $T$ and $E$ dependence fits the description $$R_{\mathrm{escape}}{\mathrm{\hspace{0.17em}=\hspace{0.17em}e}}^2\mathrm{\hspace{0.17em}/\hspace{0.17em}\epsilon (kT\hspace{0.17em}+\hspace{0.17em}g\lambda \prime Ee)}$$ where $g$ is a geometric factor and ${\text{gλ′5\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−7}}$ cm (which implies λ′∼10² Å for energy gained from the field), while (1) and (2) together account for the $E$ dependence. The integral distribution function is $${\mathrm{P(R)\hspace{0.17em}=\hspace{0.17em}(R\hspace{0.17em}/\hspace{0.17em}R}}_m{)}^{\text{−2.7}}$$ for separation $\mathrm{\ge R}$ , with $\text{P\hspace{0.17em}=\hspace{0.17em}1}$ at $R_m\text{≅100 Å}$ . It is shown that many electron reactions in organic liquids and glasses fit a common concentration dependence, which is predictable from (3). It is also shown that in the region of ∼ 10⁻⁴ − 10⁻¹ M solute in water, the yield of chemical reduction obeys the same concentration dependence as liquid alkanes. This effect is attributed to a population of electrons which are not trapped and do not become hydrated. Consequently their electrical behavior depends upon the high‐frequency dielectric constant, accounting for similar behavior in cyclohexane and in water.