Molecular shape effects on electron and ion behavior in dielectric liquids: cis- and trans-butene-2 between the freezing and critical points

Abstract

Radiolysis free ion yields, electron mobilities, and ion mobilities were measured as functions of applied electric field strength in the liquids cis- and trans-butene-2 at temperatures from near their freezing points to near their critical points. The dielectric permittivities were also measured, to permit extraction of electron thermalization distances from free ion yield data. The thermalization distance distribution in each liquid was found to be the Gaussian YGP, rather than the exponential YE or YEP. This indicates that electrons are not captured before thermalization in either liquid. The density-normalized thermalization distances bGPd were ∼40% larger in cis- than in trans-butene-2; this correlates with the more globular structure of the cis- molecules, which decreases the efficiency of electron energy loss collisions in the liquid phase. Electron mobilities were not appreciably different from those reported earlier. Cation mobilities in the liquids from the freezing points (T/Tc ≈ 0.35, d/dc ≈ 3.2 ) up to ∼400 K (T/Tc ≈ 0.92, d/dc ≈ 2.0) are adequately described by the free-volume model. At densities d/dc < 2.0 the mobilities are smaller than predicted by the free-volume model.