Full-dimensional quantum scattering calculations of rovibrationally excited HD+HD collisions

Collisions of H₂ and its deuterated counterpart HD play a crucial role in the chemistry of the early universe, cold interstellar media (ISM), star forming regions, and planetary atmospheres. These systems also serve as prototypes for quantum calculations of diatom-diatom collisions. Here, we report full-dimensional quantum scattering calculations of ro-vibrational transitions in HD+HD collisions on a highly accurate interaction potential for the H₂-H₂ system. The computed results are in agreement with total cross sections reported in previous experimental results, including resonant features in the energy dependence of the cross section. In particular, low-energy cross sections show a strong resonant feature associated with an l=3 partial wave in the incident channel. Several near-resonant ro-vibrational transitions are identified that conserve the overall rotational angular momentum and nearly conserve the internal energy of the collision partners.