Prospects for producing ultracoldNH3molecules by sympathetic cooling: A survey of interaction potentials

Abstract

We investigate the possibility of producing ultracold $\mathrm{N}{\mathrm{H}}_{3}$ molecules by sympathetic cooling in a bath of ultracold atoms. We consider the interactions of $\mathrm{N}{\mathrm{H}}_{3}$ with alkali-metal and alkaline-earth-metal atoms, and with Xe, using ab initio coupled-cluster calculations. For $\mathrm{Rb}\text{\ensuremath{-}}\mathrm{N}{\mathrm{H}}_{3}$ and $\mathrm{Xe}\text{\ensuremath{-}}\mathrm{N}{\mathrm{H}}_{3}$ we develop full potential energy surfaces, while for the other systems we characterize the stationary points (global and local minima and saddle points). We also calculate isotropic and anisotropic van der Waals ${C}_{6}$ coefficients for all the systems. The potential energy surfaces for interaction of $\mathrm{N}{\mathrm{H}}_{3}$ with alkali-metal and alkaline-earth-metal atoms all show deep potential wells and strong anisotropies. The well depths vary from $887\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ for $\mathrm{Mg}\text{\ensuremath{-}}\mathrm{N}{\mathrm{H}}_{3}$ to $5104\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ for $\mathrm{Li}\text{\ensuremath{-}}\mathrm{N}{\mathrm{H}}_{3}$. This suggests that all these systems will exhibit strong inelasticity whenever inelastic collisions are energetically allowed and that sympathetic cooling will work only when both the atoms and the molecules are already in their lowest internal states. $\mathrm{Xe}\text{\ensuremath{-}}\mathrm{N}{\mathrm{H}}_{3}$ is more weakly bound and less anisotropic.