Coupled channel study of rotational excitation of H₂ by Li+ collisions

Integral cross sections for rotational excitation of H2 by Li+ impact have been computed in a coupled channel formalism for the energy range 0.05-0.5 eV. Computational results are reported for the rigid rotator, "energy corrected" rigid rotator, and vibrating rotator models (the latter using accurate numerical vibrational functions of the Kolos-Wolniewicz potential including adiabatic correction). The "energy corrected" model, which adjusts the energy levels of the rigid rotator to agree closely with the experimental levels of the diatomic molecule by inclusion of the centrifugal distortion term, affords a noticeable improvement over the usual rigid rotator approximation for H2 with no increase in computational effort. Comparison with the classical rigid rotator results of LaBudde and Bernstein [J. Chem. Phys. 59, 3687 (1973)] show reasonable agreement with the present rigid rotator cross sections retaining open channels only. Peaks are obtained in the partial integral cross section in the threshold region for the (a) 0 → 2 transition (0.05 eV), (b) 0→4 transition (0.15 eV), and (c) 0 → 6 transition (0.3 eV). For 0 → 4,6 excitations, indirect transitions make the dominate contribution to the cross sections.