Free ion yields, electron thermalization distances, and ion mobilities in liquid cyclic hydrocarbons: Cyclohexane and t r a n s- and c i s-decalin

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Abstract
Free ion yields GEfi were measured as a function of electric field strength E in liquids of the cyclic hydrocarbons cyclohexane, trans‐decalin, and cis‐decalin at temperatures up to 514, 386, and 372 K, respectively. By comparing the measured GEfi to values calculated using the extended Onsager model, zero‐field free ion yields G0fi and thermalization distances bGP were obtained. The values of G0fi in trans‐decalin were used to correct previously reported values of the electron mobility obtained using estimates of G0fi. Values of the density‐normalized thermalization distances bGPd were ∼9% higher than in the linear n‐alkanes, that is, at a given reduced density d/dc, energy transfer from the thermalizing electron is less efficient than to the n‐alkanes. Measured molecular cation mobilities μ+ were correlated with liquid viscosity and compared with neutral molecule diffusion coefficients. The mobility of the molecular cations was three to four times smaller than that of the corresponding neutral molecules. A free volume model was used to describe the temperature dependence of μ+. Ion transport in a liquid is made easier by increasing the free volume of the liquid, which occurs when it is heated under its vapor pressure. The amount of thermal energy required to activate the actual transport of the ions is considerably smaller than suggested by the Arrhenius model.