Quantum tunnelling reactions play an important role in chemistry when classical pathways are energetically forbidden¹, be it in gas-phase reactions, surface diffusion or liquid-phase chemistry. In general, such tunnelling reactions are challenging to calculate theoretically, given the high dimensionality of the quantum dynamics, and also very difficult to identify experimentally^2,3,4. Hydrogenic systems, however, allow for accurate first-principles calculations. In this way the rate of the gas-phase proton-transfer tunnelling reaction of hydrogen molecules with deuterium anions, H₂ + D⁻ → H⁻ + HD, has been calculated⁵, 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) × 10⁻²⁰ cm³ s⁻¹. This measured value agrees with quantum tunnelling 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 H₂ densities, can be traced back to previously unobserved heating dynamics in radiofrequency ion traps.

当经典途径被能量禁止时，量子隧道反应在化学中发挥着重要作用¹，无论是在气相反应、表面扩散还是液相化学中。一般来说，考虑到量子动力学的高维性，这种隧道反应在理论上很难计算，而且也很难通过实验来识别^2,3,4。然而，氢系统可以进行准确的第一原理计算。这样就 计算出了氢分子与氘阴离子的气相质子转移隧道反应的速率H ₂  + D ⁻  → H ^{− + HD 5}，但至今缺乏实验验证。在这里，我们展示了在低温 22 极离子阱中进行的反应速率的高灵敏度测量。我们观察到极低的速率常数 (5.2 ± 1.6) × 10 ⁻²⁰  cm ³  s ^{− 1}。该测量值与量子隧道计算一致，可作为分子理论的基准并促进对基本碰撞过程的理解。_{在高H 2}密度下观察到的反应速率与线性比例的偏差可以追溯到射频离子阱中之前未观察到的加热动力学。