Test of the Li+–He interaction potential

Abstract

The mobility of Li+ ions in He has been measured at a gas temperature of 300 °K over a wide range of E/N, where E is the electric field intensity and N is the gas number density. A new theory of ion mobility is used to calculate from these data the standard Ω integral ?(1,1) of kinetic theory for Li+ in He over a range of effective gas temperature extending from 300 to 28 700 °K. The ab initio quantum mechanical interaction potential for the Li+–He system computed by Catlow et al. is also used to calculate ?(1,1) as a function of Teff. A comparison of the two sets of data serves as a test of the Catlow potential. The test is extended to still higher effective temperatures (up to 60 000 °K) by comparison with values of ?(1,1) computed from the short-range repulsive potential derived from Li+ beam scattering experiments in helium. The Catlow potential reproduces the general features of the dependence of the ’’experimental’’ Ω integral on Teff over the entire range of the test. However, significant discrepancies exist; they could be resolved by making substantial alterations in the Catlow potential in the region of short ion–atom separation distance and smaller adjustments in the region of the potential minimum.