Effect of an external electric field on the yield of free ions. IV. Epithermal electron scavenging in neopentane

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Abstract
It has been rigorously shown that, in the Onsager model, the probability of a pair of ions escaping geminate neutralization is independent of charge scavenging irrespective of the nature of the escaping ions provided only that scavenging follows thermalization. Thus the experimental evidence that a small concentration of SF6 drastically reduces the free−ion yield in neopentane in the presence of an external field (Schmidt) is taken to demonstrate epithermal electron scavenging in neopentane. Corroborative evidence is found in substantial reduction of free−ion yield in neopentane with relatively small concentrations of CCl4 and CS2 in the absence of an external field (Schmidt and Allen). On the basis of a theoretical treatment presented in this paper, the cross sections of epithermal electron attachment in neopentane are found to be 4×10−16, 5×10−17, and 1×10−18 cm2, respectively, for SF6, CCl4, and CS2. These values are obtained on analyzing the relevant experiments on free−ion yields according to the present theory. Comparison with gas−phase cross sections is attempted.