Interaction potential, transport properties, and velocity distributions of Na+ ions in Ne

Abstract

Comparisons of experimentally measured transport properties with values determined from calculations based on three-temperature-kinetic theory, on bi-Maxwellian kinetic theory, and on Monte Carlo simulations have established that the Na+-Ne interaction potential of Koutselos, Mason, and Viehland [J. Chem. Phys. 93, 7125 (1990)] is a close approximation to the true potential. (In the bi-Maxwellian approach, the ions are modeled in first-approximation as a large fraction that behaves according to a low-temperature Maxwell distribution and a small fraction that follows one of higher temperature; the true distribution is computed from these by a weighted-residual method.) This potential was then used to compute velocity distribution functions of Na+ ions in room-temperature Ne at widely different average ion energies. The skewness of the distributions in the direction of the electric field initially increased rapidly with increasing energy, and then slowly decreased, as did the excess kurtosis both parallel and perpendicular to the electric-field direction. It was clearly established that there is correlation between the perpendicular and parallel velocity-component distribution functions and that the correlation increases with increasing average ion energy. © 1992 The American Physical Society.