Effect of Electron Scavengers on the Positive Ion Reactions in the Radiolysis of Cyclopropane Solutions

Abstract

Electron scavengers such as CCl₄, SF₆, N₂O and CH₃Br are found to increase the yield of the secondary positive ion reactions which occur in the radiolysis of cyclopropane solutions in cyclohexane. The observed increase can be understood in terms of an increase in the lifetime of the ion pairs which results when the electron initially formed is converted to a less mobile negative ion. The quantitative aspects can be treated in terms of the change in the mutual diffusion coefficient of the ion pair if one includes in the model the concentration dependence for ion scavenging found when only one solute is present. In the present study electron capture by CCl₄ is found to result in a decrease in the diffusion coefficient of the ions by a factor of 17. From this and available experimental information on the diffusion coefficients of positive and massive negative ions the diffusion coefficient of the negative entity initially produced by the radiation in cyclohexane is estimated as 2.6 × 10⁻⁴ cm²sec⁻¹. This diffusion coefficient is considerably higher than those for the massive negative ions so that there seems to be little question but that the electron is involved in a more or less free state. The absolute rate constant for the electron scavenging process is estimated to be of the order of magnitude of ${10}^{11}{M}^{\text{−1}}·{\sec }^{\text{−1}}$ and that for the positive ion reactions of cyclopropane a factor of 30 smaller.