Transport coefficients and interaction potentials for lithium ions in helium and argon

A new approach to the calculation of ion swarm parameters has been developed, based upon a Kramers-Moyal expansion of the Boltzmann collision integral, and has made it possible to avoid the convergence problems associated with the so-called two- and three-temperature theories. The new approach has been used, together with new experimental data, to investigate the 7 Li + -He and 7 Li + -Ar systems. For the 7 Li + -He system, excellent agreement is found between the experimental data and data calculated from a recent ab initio potential. For the 7 Li + -Ar system, a similarly good agreement is found when the best available ab initio potential is modified in a direction indicated by theoretical considerations.