Electron mobilities in fluids through the liquid and critical regions: isomeric butenes

Abstract

Electron mobilities are similar in all four isomeric butenes near the critical region, ∼ 10 cm2/V s at ∼420 K, and again in the low temperature liquids, ∼10−3 cm2/V s at ∼ 150 K, but not at intermediate temperatures. The Arrhenius temperature coefficient of the mobility decreases with increasing temperature in cis-butene-2 and isobutene, and increases with temperature in butene-1 and trans-butene-2. This difference in behavior is reflected in the temperature dependence of the dispersion parameter σ in the assumed Gaussian distribution of transition energies between localized and extended states. The extreme cases are trans-butene-2, for which dσ/dT = 0, and cis-butene-2, for which dσ/dT ≈ (2kCp)1/2. Mobilities in mixtures of cis- and trans-butene-2 do not display ideal solution behavior; the transition energies E0 go through a maximum. The mobility in liquid cis-butene-2 under its vapor pressure goes through a maximum value of 17 cm2/V s at 426 K, decreases to 14 cm2/V s at Tc = 433 K, then increases with temperature in the constant density supercritical gas. Maxima are not observed in the other butenes. Electron migration in each of the supercritical gases is an activated process with an activation energy of ∼0.3 eV. The present results emphasize the large role played by phase structure in electron migration.