Cation mobilities in C1–C4 hydrocarbon gases at densities up to the critical

The temperature coefficient of cation mobility, dμ/dT, at constant gas density n, is positive and increases with increasing n. The increase of temperature coefficient is attributed to the clustering of molecules about the ion. However, the temperature coefficient is positive even for the mass-identified, unclustered CO3− ion in N2 gas (Eisele, Perkins, and McDaniel. J. Chem. Phys. 1980). The energy dependence of the cross section for the scattering of CO3− by N2 was deconvoluted from the (μn, T) data. The cross section decreases with increasing energy in a manner that implies sticky collisions (associative interactions) at energies <0.1 eV, and essentially hard core collisions at higher energies. The scattering of CH5+(?) ions by CH4 behaves similarly. The cross section in methane is larger than that predicted by the simple polarization potential at all energies. In the low density gas the ion mobility is controlled by collision with one molecule at a time, and μn ≈ constant. In the dense liquid the mobility is governed mainly by viscosity, and μη ≈ constant. The transition region is [Formula: see text], which corresponds to [Formula: see text] A plot of μη against η for several hydrocarbons ranging from methane to n-hexane is nearly independent of molecular size in both the liquid and gas phases.