Sympathetic cooling of NH(X³Σ⁻) molecules by Rb and Cs atoms at ultralow energies

The relative size of the elastic cross sections between NH molecules colliding with Cs and Rb atoms on the lowest potential energy surfaces of spin-stretched quartet symmetry are computed using the full quantum treatment and taking the target molecule to be in its ground rotational state. Results are compared between the two systems under similar dynamics and the Rb atom is found to yield larger cross sections at ultralow energies. The process is seen to be dominated by dispersion interaction and an analysis of the effects on the cross sections induced by changes on the C₆ coefficients is carried out in detail for both systems.