Collisions of NH(3Σ-) with Rb and Cs at ultralow energies:: A quantum study of rotational cooling efficiency

Using ab initio calculations for the lowest, spin-stretched, quartet potential energy surfaces for Rb and Cs neutral atoms interacting with the NH((3)Sigma(-)) polar target, the cold collision quantum dynamics is analyzed at ultralow energies to examine possible propensity rules existing for the relaxation of either spin or rotational target states (or both) via sympathetic cooling induced by the partner atoms. The specific coupling of Hund's case (b) is adopted for the dynamical treatment of spin and rotational angular momenta and the coupled channel approach is employed to solve the scattering equations. Both rotational and/or spin relaxation cross sections are obtained down to 10(-6) cm(-1) of energy and corresponding cooling rates are analyzed and compared between the two systems.