Nonadiabatic collisions of CaH with Li: Importance of spin-orbit-induced spin relaxation in spin-polarized sympathetic cooling of CaH.

We apply our recently developed, quantum, nonadiabatic, two-dimensional finite element method [ Warehime etal., J. Chem. Phys. 142,034108 (2015).] to estimate the probability of the nonadiabatic reaction in spin-polarized Li(²S) + CaH(²Σ+). This spin-orbit-induced reaction leads to trap loss due to the opening of a barrierless pathway to the Ca(¹S) + LiH(¹Σ+) products. To investigate this reaction we calculate three two-dimensional radial cuts of the potential energy surfaces for the triplet and singlet electronic states. We also calculate the spin-orbit coupling matrix element between these two electronic states. From our nonadiabatic scattering calculations we estimate the spin-flip probability in the sympathetic cooling of the CaH molecule with ultracold Li atoms to be small: on the order of 10-7 and increasing to 10-4 at higher temperatures. We estimate the order of the rate constant in our reduced dimensionality approach for the reaction proceeding on the singlet potential at a temperature of t K to be 10-10 cm³/s. This is of the same order as the measured value of 3.6 x 10-10 cm³/s [Singh et al., Phys. Rev. Lett. 108, 203201 (2012)]. This reaction rate is at least seven orders of magnitude larger than our estimated rate of the spin-orbit-induced triplet to singlet reaction. Our nonadiabatic result is encouraging for the experimental prospects for this title system. [ABSTRACT FROM AUTHOR]