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

Abstract

JEAN-POL DODELET and GORDON R. FREEMAN. Can. J. Chem. 55,2893(1977. Electron mobilities are similar in all four isomeric butenes near the critical region, N 10 cm2/V s at -420 K, and again in the low temperature liquids, -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 o in the assumed Gaussian distribution of transition energies between localized and extended states. The extreme cases are trans-butene-2, for which do/dT = 0, and cis-butene-2, for which do/dT z (2kCp)'12. Mobilities in mixtures of cis-and trans-butene-2 do not display ideal solution behavior; the transition energies Eo go through a maximum. The mobility in liruid 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 T, = 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 . 3eV. The present results emphasize the large role played by phase structure in electron migration.JEAN-POL DODELET et GORDON R. FREEMAN. Can. J. Chem. 55,2893(1977. Les mobilitts Blectroniques des quatre isomeres du butene sont semblables pres de la region critique: -10 cm2/V s a -420 K, ainsi qu'en phase liquide a basse temperature: N cm2/.V s a -150 K. Toutefois, ces mobilitks different dans la region des temperatures intermediaires. Pour ces mobilitks, le coefficient de temperature d'Arrh6nius decroit en augmentant la temperature du cis-butene-2 et de l'isobutene tandis qu'il augmente en Blevant la temperature du buthe-1 et du trans-buthe-2. Cette difference de comportement se refl&te dans la variation de o avec la temperature. o est le parametre de dispersion dans la distribution, supposk gaussienne, des transitions entre les Btats localises et Btendus d'energie. Les cas extrsmes sont le trans-buttne-2 pour lequel do/dT = 0 et le cis-butene-2 pour lequel do/dT % (2kCP)'l2. Les mobilites dans les melanges de cis-et trans-buttne-2 ne presentent pas le comportement d'une solution idkale; les energies de transition E, passent par un maximum. La mobilite dans le cisbutene-2 liquide, sous sa propre tension de vapeur, passe par un maximum de 17 cmZ/V s a 426 K pour ensuite dkroitre a 14 cmZ/V s a T, = 433 K. Dans le gaz supercritique, a densite constante, cette mobilitB augmente avec la temperature. Aucun maximum n'est observe pour les autres butbnes. La migration Blectronique pour tous ces gaz au dessus de la temperature critique est un processus accompagnk d'une Bnergie d'activation de -0.3 eV. Ces rksultats mettent l'accent sur le rBle joue par la structure de la phase dans la migration Blectronique.

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

“…The behavior in cis-butene-2 is similar to that in propane, while that in trans-butene-2 is similar to that in ethene or cyclopropane (25). Transient anion formation has been suggested to occur in the latter three liquids (5,25). Anion formation would be more favorable at the higher densities near the freezing points.…”

“…Previous measurements showed remarkable differences in the radiolytic free ion yields (3,4) and in the mobilities of thermal electrons (3,5) in these liquids. It appears that electrons are captured to form transient anions in the trans-isomer.…”

“…We therefore apply the free-volume model of ion transport (14) The lines were calculated with eq. [5], using the parameters listed in Table 4. where A+ is a constant, V is the molar volume, Vo is the molar volume at which the liquid molecules are too crowded for diffusion to occur, E+ is a residual exponential temperature coefficient (see below), and R is the gas constant. Equation [5] provided an adequate description of the ion mobilities in the liquids from their freezing points up to 400 K, above which the calculated mobilities were too high (Fig.…”

“…The parameter values obtained by fitting eq. [5] to the experimental results up to 400 K are listed in Table 4.…”