INTERATOMIC POTENTIAL AND TRANSPORT-PROPERTIES OF NA+ IONS IN HE

Hitherto unavailable experimental values of the ratio, D(T)/K, of the transverse diffusion coefficient to mobility for Na+ ions drifting in helium gas are reported. Results were obtained with estimated accuracies of better than 3% at temperatures between 302 and 304 K, and at electric field to neutral gas density ratios, E/N, ranging from 5 to 400 Td. By an independent approach, the three transport parameters are also computed by Monte Carlo simulation using the modified Tang-Toennies potential and the Koutselos, Mason and Viehland potential as input, separately. Comparison between the simulated results and available experimental data suggests that the latter potential represents fairly well the true interaction in the long and intermediate ranges, but its short-range repulsive region is too soft.