State-resolved rotational cross sections and thermal rate coefficients for at low temperatures and HD + HD elastic scattering

Results for quantum-mechanical calculations of the integral cross sections and corresponding thermal rate coefficients for para-/ortho- H 2 + HD collisions are presented. Because of significant astrophysical interest in regard to the cooling of primodial gas the low temperature limit of para-/ortho- H 2 + HD is investigated. Shape resonances in the rotational state-resolved cross sections have been calculated at low energies. These resonances are important and significantly contribute to the corresponding rotational state-resolved thermal rate coefficients, particularly at low temperatures T ≲ 100 K . Additionally, the cross sections for elastic HD + HD have been calculated. As compared to the two other calculations for H 2 + HD we obtained mixed results, confirming one case but differing in the second case. In our treatment of HD + HD we obtained satisfactory agreement with both theoretical and experimental expectations.