Kinetics of Electron Scavenging and Ion Recombination in the Radiolysis of Hydrocarbon Solutions

Abstract

A functional description of the lifetimes of the ion pairs produced in the radiolysis of pure hydrocarbons is derived from the concentration dependence observed for ion scavenging. A number of consequences which follow from this description are explored. In particular it is shown that in the absence of scavenger the decay of the geminate ions must be very closely described by ${\mathrm{F(t)\hspace{0.17em}=\hspace{0.17em}e}}^{\mathrm{\lambda t}}\mathrm{erfc}{\mathrm{(\lambda t)}}^{\text{1/2}}$ , where $\lambda$ is a constant and $\mathrm{F(t)}$ is the fraction of ions present at time $t$ . Appropriate descriptions for the growth and decay of secondary ions are given, and the results are applied to real systems of finite pulses. Comparison is made between the predictions given here for the time dependence of the population of secondary negative ions and the experimental observations of Thomas and co‐workers on the decay of diphenylide negative ion in pulse irradiated cyclohexane solutions of diphenyl. From this comparison it is concluded that the rate constant for electron scavenging by the diphenyl is ${\text{∼\hspace{0.17em}3\hspace{0.17em}×\hspace{0.17em}10}}^{11}{M}^{\text{−1}}·{\sec }^{\text{−1}}$ and that the preponderant fraction of ion recombination occurs in the time region of 10⁻¹¹–10⁻⁹ sec.