非常慢的离子-分子反应中的隧道效应
Tunneling in a very slow ion-molecule reaction
摘要：
量子隧穿反应在化学中起着重要的作用，当经典的途径是大力禁止，无论是在气相反应，表面扩散，或液相化学。一般来说，这样的隧穿反应在理论上是很难计算的，因为量子动力学的维数很高，而且也很难在实验上确定。然而，产氢系统允许精确的第一性原理计算。用这种方法计算了氢分子与氘阴离子的气相质子转移隧穿反应速率H_2 + D^-> H^- + HD，但至今缺乏实验验证。在这里，我们提出了高灵敏度的反应速率的测量进行了低温22极离子阱。我们观察到一个极低的速率常数，为（5.2 ± 1.6）× 10^（-20）cm ^3/s。这个测量值与量子隧穿计算一致，作为分子理论的基准，并推进了对基本碰撞过程的理解。反应速率偏离线性标度，这是在高H_2密度下观察到的，可以追溯到以前未观察到的射频离子阱中的加热动力学。
英文摘要：
Quantum tunneling reactions play a significant role in chemistry when classical pathways are energetically forbidden, be it in gas phase reactions, surface diffusion, or liquid phase chemistry. In general, such tunneling reactions are challenging to calculate theoretically, given the high dimensionality of the quantum dynamics, and also very difficult to identify experimentally. Hydrogenic systems, however, allow for accurate first-principles calculations. In this way the rate of the gas phase proton transfer tunneling reaction of hydrogen molecules with deuterium anions, H_2 + D^- --> H^- + HD, has been calculated, but has so far lacked experimental verification. Here we present high-sensitivity measurements of the reaction rate carried out in a cryogenic 22-pole ion trap. We observe an extremely low rate constant of (5.2 +- 1.6) x 10^(-20) cm^3/s. This measured value agrees with quantum tunneling calculations, serving as a benchmark for molecular theory and advancing the understanding of fundamental collision processes. A deviation of the reaction rate from linear scaling, which is observed at high H_2 densities, can be traced back to previously unobserved heating dynamics in radiofrequency ion traps.
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