Dependence of Radiation-Induced Conductance of Liquid Hydrocarbons on Molecular Structure

The radiolytic ion mobilities u, ion-neutralization rate constant k, steady-state radiation-induced conductance κ, and free-ion yield Gfi have been measured for a number of saturated hydrocarbon liquids of different molecular shape. The values of G>fi in the following liquids at 20° were; cyclohexane, 0.11; n-hexane, 0.11; n-pentane, 0.12; 2,2-dimethylbutane, 0.40; 2,2-dimethylpropane, 0.81. The unusually high values for the last two compounds were partly associated with a current “overshoot” that occurred at the beginning of current-vs-time oscillograms that were obtained for the evaluation of k / u. The overshoot was not present in oscillograms obtained from the first three liquids. The causes of the overshoot and the high Gfi values are not known, but their magnitudes correlate with the closeness to spherical shape of the molecules. The facility of electron trapping and of electron energy loss in the subvibrational-excitation energy region are probably dependent on molecular shape and on liquid structure, in addition to electron affinities and dipole moments. The overshoot was eliminated and Gfi was reduced by adding an electron scavenger to 2,2-dimethylbutane or 2,2-dimethylpropane. Electron scavengers had little or no effect on the other liquids.