Is Quantum Above-Barrier Reflection Important for Molecular Barrier Crossing Rates?,Journal of Chemical Theory and Computation

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Is Quantum Above-Barrier Reflection Important for Molecular Barrier Crossing Rates?
Journal of Chemical Theory and Computation ( IF 5.7 ) Pub Date : 2024-09-11 , DOI: 10.1021/acs.jctc.4c00917
Chiara Aieta ₁ , Michele Ceotto ₁ , Eli Pollak ₂

Affiliation

Understanding quantum tunneling and above-barrier reflection effects on unimolecular and bimolecular reaction rate constants remains challenging to this very day. In many applications, especially when considering moderate-to-high temperatures, the “standard” procedure is to use the parabolic barrier approximation. Recent work has shown though that this may be insufficient, and one cannot ignore anharmonicity. In this work, we study the analytic theory, including anharmonicity obtained when expanding the thermal rate up to order ℏ⁴. Such theories need high-order derivatives of the potential at the barrier top. We show that such derivatives are computed straightforwardly for six different reactions. We suggest a straightforward methodology for assessing whether the parabolic barrier approximation is valid and show that when the reaction asymmetry is large, this may lead to significant quantum above-barrier reflection and transmission coefficients, which are less than unity.

中文翻译：

量子势垒之上反射对于分子势垒穿越率重要吗？

直到今天，了解量子隧道效应和势垒以上反射对单分子和双分子反应速率常数的影响仍然具有挑战性。在许多应用中，特别是在考虑中高温时，“标准”程序是使用抛物线势垒近似。但最近的研究表明，这可能还不够，而且我们不能忽视不和谐性。在这项工作中，我们研究了解析理论，包括将热速率扩展到ℏ ⁴量级时获得的非谐性。这些理论需要势垒顶部势能的高阶导数。我们表明，可以直接计算六种不同反应的此类导数。我们提出了一种简单的方法来评估抛物线势垒近似是否有效，并表明当反应不对称性很大时，这可能会导致显着的量子势垒上方反射和透射系数，这些系数小于1。

更新日期：2024-09-11

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