Theoretical Answers to Some Experimental Questions about Gaseous Ion Transport
Larry A. Viehland
Australian Journal of Physics
50(3) 671 - 682
AbstractIt is shown that the diffusion coefficients parallel to the electric field in an ion swarm experiment are greater than the perpendicular diffusion coefficients at low values of E/N, the ratio of the electric field strength to the gas number density, but that at high E/N the two are approximately equal or the inequality is reversed. For electron swarms the inequalities are the reverse of those for ion swarms, unless there is a significant Ramsauer minimum in the momentum-transfer cross section. A second point is that for many ion–atom systems the zero-field mobility is not close to its polarisation limit even when the gas temperature is 4.35 K. It is also shown that the unusual mobilities observed for Ar+ ions in He gas at 4.35 K are not due to quantum-mechanical (resonant scattering) effects as postulated by the experimenters. Finally, it is shown that it is possible to compute gaseous ion transport coefficients for molecular ions from a knowledge of the fundamental interaction potentials rather than from assumed models for the cross sections.
© CSIRO 1997