Ultracold collisions between two light indistinguishable diatomic molecules: elastic and rotational energy transfer in HD+HD
Abstract
A close coupling quantum-mechanical calculation is performed for rotational energy transfer in a HD+HD collision at very low energy, down to the ultracold temperatures: T 10-8 K. A global six-dimensional H2-H2 potential energy surface is adopted from a previous work [Boothroyd et al., J. Chem. Phys., 116, 666 (2002).] State-resolved integral cross sections σij→ i'j'(kin) of different quantum-mechanical rotational transitions ij→ i'j' in the HD molecules and corresponding state-resolved thermal rate coefficients kij→ i'j'(T) have been computed. Additionally, for comparison, H2+H2 calculations for a few selected rotational transitions have also been performed. The hydrogen and deuterated hydrogen molecules are treated as rigid rotors in this work. A pronounced isotope effect is identified in the cross sections of these collisions at low and ultracold temperatures.