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

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.