Laude Gabriel, Calderini Danilo, Welsch Ralph, Richardson Jeremy O
Laboratory of Physical Chemistry, ETH Zürich, Switzerland.
Phys Chem Chem Phys. 2020 Aug 7;22(29):16843-16854. doi: 10.1039/d0cp01346c. Epub 2020 Jul 15.
Thermal rate constants for Mu + CH, Mu + CH and Mu + CH and their equivalent reactions with H were evaluated with ab initio instanton rate theory. The potential-energy surfaces are fitted using Gaussian process regression to high-level electronic-structure calculations evaluated around the tunnelling pathway. This method was able to successfully reproduce various experimental measurements for the rate constant of these reactions. However, it was not able to reproduce the faster-than-expected rate of Mu + CH at 300 K reported by Fleming et al. [Phys. Chem. Chem. Phys., 2015, 17, 19901 and Phys. Chem. Chem. Phys., 2020, 22, 6326]. Analysis of our results indicates that the kinetic isotope effect at this temperature is not significantly influenced by quantum tunnelling. We consider many possible factors for the discrepancy between theory and experiment but conclude that in each case, the instanton approximation is unlikely to be the cause of the error. This is in part based on the good agreement we find between the instanton predictions and new multiconfigurational time-dependent Hartree (MCTDH) calculations for Mu + CH using the same potential-energy surface. Further experiments will therefore be needed to resolve this issue.
利用从头算瞬子速率理论评估了Mu + CH、Mu + CH和Mu + CH及其与H的等效反应的热速率常数。使用高斯过程回归将势能面拟合到围绕隧穿路径评估的高水平电子结构计算中。该方法能够成功再现这些反应速率常数的各种实验测量结果。然而，它无法再现Fleming等人[《物理化学化学物理》，2015年，17，19901和《物理化学化学物理》，2020年，22，6326]报道的300 K时Mu + CH比预期更快的反应速率。对我们结果的分析表明，该温度下的动力学同位素效应不受量子隧穿的显著影响。我们考虑了理论与实验之间差异的许多可能因素，但得出结论，在每种情况下，瞬子近似不太可能是误差的原因。这部分是基于我们发现的瞬子预测与使用相同势能面的Mu + CH的新的多组态含时Hartree（MCTDH）计算之间的良好一致性。因此，需要进一步的实验来解决这个问题。
