JILA, NIST and University of Colorado, Department of Physics, University of Colorado, Boulder, CO 80309, USA.
Science. 2010 Feb 12;327(5967):853-7. doi: 10.1126/science.1184121.
How does a chemical reaction proceed at ultralow temperatures? Can simple quantum mechanical rules such as quantum statistics, single partial-wave scattering, and quantum threshold laws provide a clear understanding of the molecular reactivity under a vanishing collision energy? Starting with an optically trapped near-quantum-degenerate gas of polar 40K87Rb molecules prepared in their absolute ground state, we report experimental evidence for exothermic atom-exchange chemical reactions. When these fermionic molecules were prepared in a single quantum state at a temperature of a few hundred nanokelvin, we observed p-wave-dominated quantum threshold collisions arising from tunneling through an angular momentum barrier followed by a short-range chemical reaction with a probability near unity. When these molecules were prepared in two different internal states or when molecules and atoms were brought together, the reaction rates were enhanced by a factor of 10 to 100 as a result of s-wave scattering, which does not have a centrifugal barrier. The measured rates agree with predicted universal loss rates related to the two-body van der Waals length.
化学反应如何在超低温度下进行？简单的量子力学规则，如量子统计、单分波散射和量子阈定律，能否为消失的碰撞能下的分子反应性提供清晰的理解？我们从光学捕获的近量子简并的极性 40K87Rb 分子气体开始，这些分子被制备在绝对基态，我们报告了放热原子交换化学反应的实验证据。当这些费米子分子在几百纳米开尔文的温度下被制备在单一量子态时，我们观察到了由通过角动量势垒的隧道引起的 p 波主导的量子阈碰撞，随后是接近 1 的短程化学反应概率。当这些分子被制备在两个不同的内部状态时，或者当分子和原子被聚集在一起时，由于 s 波散射，反应速率提高了 10 到 100 倍，因为 s 波散射没有离心势垒。测量的速率与与双体范德华长度相关的预测通用损耗速率一致。
