The Li⁺-H₂system in a rigid-rotor approximation: potential energy surface and transport coefficients

An accurate potential energy surface for the Li + –H2 system has been calculated ab initio at an H–H distance of 1.449 a0, using an extended geminal model. The potential has been used to find elastic and inelastic total and transport cross sections, which have subsequently been used in moment-type transport calculations with a Kramers–Moyal-type expansion of the collision integral. The ion mobilities have also been measured at 295 K and E/n0 values from 10 to 450 Td, which corresponds to mean centre-of-mass energies from 0.04 to 7 eV. The agreement between experimental and calculated values is excellent below 220 Td. At higher E/n0 values, the agreement deteriorates gradually, possibly because of the neglect of vibrational excitation.