LiH−(X2Σ+)+3,4He rotational quenching at ultralow energies: spin-flip and isotopic effects from quantum dynamics on an ionic system

Abstract

We study in this work the quantum scattering between a helium atom and a LiH− molecule at low and ultralow energies. For the noble gas we have considered the two natural isotopes 3He, 4He, plus a “mock” 3.5He. Our aim is to clarify the role played by the isotopic changes of the mass in the buffer gas (in this case, helium) during collision events where the interaction is described through a newly computed ab initio rigid rotor potential between He and LiH−. The main conclusion of the present study is that this anionic species could be a good candidate for He-driven sympathetic cooling in traps since its elastic cross sections are always found to be larger than the inelastic ones in a relevant range of nearly vanishing energies. The 3He isotope is found to be more efficient than the other examples, yielding larger quenching rates in comparison with its heavier counterparts. Spin-flip inelastic channels are also analysed and discussed in terms of their dependence on the present, weak, interaction potential between partners and found to provide a further, interesting feature of the present mixture. The new results are also compared with those found by us in earlier, similar, quantum calculations on different systems.