Inelastic contributions to ion–molecule diffusion cross sections: Li+–H2

We examine the role played by inelastic collisions in the diffusion of Li+ ions in H2. Explicit expressions are derived for partial diffusion cross sections corresponding to j=0→j′=0,2 transitions. These are used, along with the results of close-coupling calculations, to demonstrate that virtual rotational coupling results in a significant enhancement of the 0→0 diffusion cross section at low energy. The total diffusion cross section and the corresponding collision integral are larger than predicted by a purely elastic calculation based on the spherically symmetric component in the intermolecular potential. This discrepancy might be significant enough to be detected in drift tube experiments.