缓冲气体阱中范德华分子的形成和动力学
Formation and dynamics of van der Waals molecules in buffer-gas traps
摘要：
我们表明，弱结合的含氦范德华分子可以产生和磁捕获的缓冲气体冷却实验，并提供了一个一般的模型，这些分子的形成和动力学。我们的分析表明，在典型的实验参数下，热力学有利于形成由氦原子与大多数开壳层原子和分子结合组成的范德华络合物，并且络合物的形成速度足够快，以确保化学平衡。对于由He原子和S态原子组成的分子对，分子自旋在形成、解离和碰撞期间是稳定的，因此这些分子可以被磁性捕获。碰撞自旋弛豫太慢，不会影响陷阱寿命。然而，含氦-3的复合物可以改变自旋，由于绝热交叉之间的捕获和未捕获的塞曼状态，介导的各向异性超精细相互作用，造成陷阱损失。我们提供了一个详细的模型为Ag 3 He分子，使用从头计算的Ag-He相互作用势和自旋相互作用，量子散射理论，并直接蒙特卡罗模拟来描述在这个系统中的形成和自旋弛豫。计算的自旋变化率同意定量与实验观察，缓冲气体冷却磁阱中的分子形成提供间接证据。
英文摘要：
We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, helium-3-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps.
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