Electron thermalization distances and free-ion yields in dense gaseous and liquid benzene

Abstract

Electron thermalization has been studied in gaseous and liquid benzene at 4.1 ≤ d/kg m−3 ≤ 878 (temperatures 295–560 K) using measurements of the free-ion yield [Formula: see text] as a function of electric field strength E and temperature T. The measured [Formula: see text] values at each T were compared to those calculated using an extended Onsager model. Assumption of a three-dimensional Gaussian distribution of secondary electron thermalization distances YG resulted in too large a field dependence. The Gaussian with the small added tail, YGP, gave the correct dependence. Values of the yield extrapolated to zero field, [Formula: see text] and of the most probable thermalization distance bGP were obtained. Variation of the density-normalized distance bGPd with reduced density d/dc (dc = critical fluid density) was expected to be similar to that in ethene, due to the π-electrons in the two compounds. Instead, it was similar to that in ethane. Throughout the liquid range, epithermal electrons were de-energized less efficiently than in the gas at d < 0.5 dc where the benzene molecules are further apart. As the density increases above 2 dc the values of bGPd decreased as in other hydrocarbons, rather than like those in hexafluorobenzene, which increased sharply. Dielectric constants were also measured up to 560 K.