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 5 d/kg m-3 5 878 (temperatures 295-560 K) using measurements of the free-ion yield G; as a function of electric field strength E and temperature T. The measured (G;, E) 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, G:, and of the most probable thermalization distance bGp were obtained. Variation of the density-normalized distance bG& with reduced density d/d, (d, = critical fluid density) was expected to be similar to that in ethene, due to the T-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 d, the values of bG& decreased as in other hydrocarbons, rather than like those in hexafluorobenzene, which increased sharply. Dielectric constants were also measured up to 560 K. On a obtenu les valeurs des rendements extrapolCs jusqu'h un champ nu], G:, ainsi que la distance de thermalisation la plus probable, bGp. A cause de la presence d'Clectrons T dans les deux systkmes, on s'attendait a ce que la variation de la distance normaliske pour la densitt, bGpd, en fonction de la densit6 rCduite, d/d,(d, = densit6 fluide critique) soit semblable 5 celle de 1'Cthtne. Toutefois, elle est semblable a celle de 1'Cthane. Dans toute la phase liquide, les Clectrons Cpithermiques perdent leur Cnergie moins facilement que dans le gaz, a d < 0,5 d,, oh les molCcules de benztne sont plus CloignCes les unes des autres. Lorsque la densit6 augmente au dessus de 2 dc, les valeurs de bGpd diminuent comme dans les autres hydrocarbures plut6t que comme dans I'hexafluorobenzkne dans lequel elles augmentent rapidement. On a aussi mesurC les constantes diClectriques jusqu'a 560 K.[Traduit par la rkdaction]

Theoretical and experimental studies of the opto-electronic properties of positively charged oligo(phenylene vinylene)s: Effects of chain length and alkoxy substitution

“…Irradiation of benzene ͑Bz͒ leads to the formation of radical cations (Bz ϩ ), excited states (Bz*), and excess electrons (e Ϫ ), [31][32][33] Bz→Bz ϩ ,Bz*,e Ϫ . ͑1͒…”

Hole Conduction along Molecular Wires: σ-Bonded Silicon Versus π-Bond-Conjugated Carbon

“…The value of E fp for benzene is also well-known with two different groups [7,8] reporting the same value of 1900 eV. Quantitative fits to the experimental data have been made by numerically solving the differential rate equations for the concentrations of Bz + , O 2 ± , and P + .…”

Highly mobile electrons and holes on isolated chains of the semiconducting polymer poly(phenylene vinylene)

“…Energy is initially absorbed from the beam mainly by the solvent, resulting in the formation of benzene radical cations ('holes'), Bz + , and excess electrons, e − . We calculated the concentration of electron-hole pairs formed in the pulse (using the known free ion yield of 0.053 per 100 eV absorbed 12,13 and the accurately measured dose) to be ϳ1 ϫ 10 Ϫ 7 M, that is, considerably less than the concentration of polymer chains in the solution.…”

“…From the end-of-pulse conductivity, and the known concentration of charge carriers, we calculate the sum of the e − and Bz + mobilities to be 0.15 cm 2 V −1 s −1 . This is very close to the value of 0.13 cm 2 V −1 s − determined by a d.c. time-of-flight method for the mobility of the excess electron 13,14 in benzene. The mobility of Bz + , which is thought to be in equilibrium with the dimer ion, Bz + 2 (ref.…”