Chemical Reactions of Li and CaH and Inelastic Ti-Ti Collisions at Cryogenic Temperatures
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A large number of cold atoms and molecules are generated using laser ablation and helium buer gas cooling. These cold atoms and molecules are used in three separate experiments. First, cold atomic Li(2S) and molecular CaH(2) are used to study gas phase chemical reactions at 1 Kelvin. The chemical reaction CaH + Li ! Ca + LiH is observed both by accelerated disappearance of CaH molecules in the presence of Li atoms and appearance of LiH molecules.Second, to investigate the role of electronic spin in a cold chemical reactions, both Li and CaH are spin polarized using optical pumping. It is observed that once the Li atoms are spin polarized, they preserve their polarization in collisions with helium buer gas. CaH molecules spin depolarize relatively quickly due to the collisions with helium. Our measurement of the CaH spin depolarization rate coecient shows astrong temperature dependence. This is attributed to the CaH population in exited rotational states.Finally, we measured the inelastic ^50 Ti-Ti collisions at 5 Kelvin. This experiment was motivated by the observed large suppression of fine structure and Zeeman state changing collisions of Ti with helium. This suppression was attributed to the titanium's submerged shell structure 3d^2 4s^2 and suggested that submerged shell might similarly suppress the Ti-Ti collisions. No such suppression was observed, and inelastic 50Ti-Ti collisions occur with a fast rate coecient as expected from titanium's anisotropic electronic potential.