Ab initio study of the neutral and anionic alkali and alkaline earth hydroxides: Electronic structure and prospects for sympathetic cooling of OH.

We have performed a systematic ab initio study on alkali and alkaline earth hydroxide neutral (MOH) and anionic (MOH-) species where M = Li, Na, K, Rb, Cs or Be, Mg, Ca, Sr, Ba. The CCSD(T) method with extended basis sets and Dirac-Fock relativistic effective core potentials for the heavier atoms has been used to study their equilibrium geometries, interaction energies, electron affinities, electric dipole moment, and potential energy surfaces. All neutral and anionic species exhibit a linear shape with the exception of BeOH, BeOH-, and MgOH-, for which the equilibrium structure is found to be bent. Our analysis shows that the alkaline earth hydroxide anions are valence-bound whereas the alkali hydroxide anions are dipole bound. In the context of sympathetic cooling of OH- by collision with ultracold alkali and alkaline earth atoms, we investigate the 2D MOH- potential energy surfaces and the associative detachment reaction M + OH→- MOH + e-, which is the only energetically allowed reactive channel in the cold regime. We discuss the implication for the sympathetic cooling of OH- and conclude that Li and K are the best candidates for an ultracold buffer gas.