Cation transport in gaseous, critical, and liquid benzene and toluene

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Abstract
The mobilities μ+ of cations in the fluids of benzene and toluene are 200–3000 fold lower than those of electrons. However, the variations of the cation mobilities with density and temperature are qualitatively similar to those of electrons, to an unexpected degree. In the liquid phase under its vapor pressure at T/Tc+∝η−x, x=1.0), but in toluene it does not (x=1.1). The ratio of the diffusion coefficients (cation/solvent molecule) is equal to about 0.25 in toluene and 0.50 in benzene. Near the critical point there is a slight maximum in μ+. The maximum is more marked in the density normalized mobility μ+n; it occurs at n/nc=2.0 in benzene and 1.6 in toluene. The mobilities in the critical fluids are 2.76×10−3 and 2.50×10−3 cm2/V s in benzene and toluene, respectively. In the low density gases the ion scattering cross sections, taken to have the form σv=Aα v−α, display α=1.4 for benzene and 1.5 for toluene. The cross sections, appropriately averaged over the Maxwellian distribution of velocities, have magnitudes similar to those expected from scattering by the r−4 polarization potential, but have a greater than expected value of α. The average ion scattering cross sections are about eightfold greater than the corresponding electron scattering cross sections. The value of μ+n in the coexistence vapor is 6.3×1018 molecule/cm V s in benzene up to n/nc=1.0, and is 6.0×1018 in toluene up to n/nc=0.15. At higher densities in the latter μ+n decreases gently, reaching (μ+n)min=4.4×1018 at n/nc=0.9. The temperature coefficient of μ+ at constant n increases with n up to nc, near the coexistence curve. The increased temperature coefficient is attributed to clustering, but the clusters are small.