Heller Eric R, Richardson Jeremy O
Laboratory of Physical Chemistry, ETH Zürich, 8093, Zürich, Switzerland.
Angew Chem Int Ed Engl. 2022 Aug 15;61(33):e202206314. doi: 10.1002/anie.202206314. Epub 2022 Jul 5.
We simulate two recent matrix-isolation experiments at cryogenic temperatures, in which a nitrene undergoes spin crossover from its triplet state to a singlet state via quantum tunnelling. We detail the failure of the commonly applied weak-coupling method (based on a linear approximation of the potentials) in describing these deep-tunnelling reactions. The more rigorous approach of semiclassical golden-rule instanton theory in conjunction with double-hybrid density-functional theory and multireference perturbation theory does, however, provide rate constants and kinetic isotope effects in good agreement with experiment. In addition, these calculations locate the optimal tunnelling pathways, which provide a molecular picture of the reaction mechanism. The reactions involve substantial heavy-atom quantum tunnelling of carbon, nitrogen and oxygen atoms, which unexpectedly even continues to play a role at room temperature.
我们模拟了两个近期在低温下进行的矩阵隔离实验，其中一个氮宾通过量子隧穿从三重态自旋交叉到单重态。我们详细说明了常用的弱耦合方法（基于势的线性近似）在描述这些深隧穿反应时的失败。然而，半经典金规则瞬子理论与双杂化密度泛函理论和多参考扰动理论相结合的更严格方法，确实提供了与实验结果高度一致的速率常数和动力学同位素效应。此外，这些计算确定了最佳隧穿途径，从而提供了反应机理的分子图像。这些反应涉及碳、氮和氧原子的大量重原子量子隧穿，出乎意料的是，这种隧穿在室温下甚至仍起作用。
