Monte-Carlo investigations of the motion of gaseous ions in electrostatic fields

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Abstract
The motion of gaseous ions in arbitrarily strong electrostatic fields has been studied by Monte-Carlo simulation techniques, assuming various forms of the ion-neutral interaction law. Approximate expressions for the mobility and the mean square velocity suggested by Wannier (1953) were in most cases found to predict the correct values within 20%. The lateral diffusion coefficient to mobility ratio Dperpendicular to / mu was in all cases studied found to be remarkably accurately connected to the mean square velocity normal to the electric field through a generalized Nernst-Townsend relation. The longitudinal diffusion coefficient D/sub /// does not, on the other hand, seem to be simply related in any way to the mean square random velocity in the field direction, except near thermal energies. For hard sphere interaction and non-vanishing fields the lateral diffusion coefficient is always larger than the longitudinal one.