Rotational alignment in collisions of Li⁺with H₂(j=0)

Fully state-selected differential and integral rotationally inelastic cross sections have been determined for the 0 →j transitions of Li+/H2 at a total energy of 0·5 eV. Results have been obtained for space frame, body frame and k 1 × k 2 frame quantization. Alignment effects are interpreted in terms of a single rainbow scattering model. A focussing effect due to the anisotropic well is found, confirming conclusions from previous classical trajectory studies. The implications of the present work for approximate methods are considered. In particular, the conventional explanation for the success of the l-dominant approximation for Li+/H2 is shown to be in error and an alternative is proposed. A discrepancy between the alignment behaviour of j = 0 →4, 6 transitions as calculated by quantum and classical mechanics is noted.