Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
J Chem Phys. 2011 Mar 28;134(12):124309. doi: 10.1063/1.3570596.
We present elastic and inelastic spin-changing cross sections for cold and ultracold NH(X (3)Σ(-)) + NH(X (3)Σ(-)) collisions, obtained from full quantum scattering calculations on an accurate ab initio quintet potential-energy surface. Although we consider only collisions in zero field, we focus on the cross sections relevant for magnetic trapping experiments. It is shown that evaporative cooling of both fermionic (14)NH and bosonic (15)NH is likely to be successful for hyperfine states that allow s-wave collisions. The calculated cross sections are very sensitive to the details of the interaction potential, due to the presence of (quasi)bound state resonances. The remaining inaccuracy of the ab initio potential-energy surface therefore gives rise to an uncertainty in the numerical cross-section values. However, based on a sampling of the uncertainty range of the ab initio calculations, we conclude that the exact potential is likely to be such that the elastic-to-inelastic cross-section ratio is sufficiently large to achieve efficient evaporative cooling. This likelihood is only weakly dependent on the size of the channel basis set used in the scattering calculations.
我们给出了冷态和超冷 NH(X (3)Σ(-)) + NH(X (3)Σ(-)) 碰撞的弹性和非弹性自旋翻转截面，这些结果是通过对精确的从头计算五重态势能面进行全量子散射计算得到的。尽管我们只考虑了零场中的碰撞，但我们关注的是与磁阱实验相关的截面。结果表明，对于允许 s 波碰撞的超精细态，两种费米子 (14)NH 和玻色子 (15)NH 的蒸发冷却都很可能成功。由于存在（准）束缚态共振，计算出的截面对相互作用势能的细节非常敏感。因此，从头计算势能面的剩余不准确性导致数值截面值存在不确定性。然而，基于对从头计算不确定性范围的抽样，我们得出结论，准确的势能很可能使得弹性到非弹性截面比足够大，从而实现有效的蒸发冷却。这种可能性仅与散射计算中使用的通道基集的大小有微弱的依赖关系。
