Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37830, United States.
Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99352, United States.
J Phys Chem B. 2020 Jul 9;124(27):5665-5675. doi: 10.1021/acs.jpcb.0c02649. Epub 2020 Jun 25.
Rate theories have found great utility across the chemical sciences by providing a physically transparent way to analyze dynamical processes. Here we demonstrate the benefits of using transition state theory and Marcus theory to study the rate of proton transfer in HCl solutions. By using long molecular dynamics simulations, we show that good agreement is obtained between these two different formulations of rate theory and how they can be used to study the pathways and lifetime of proton transfer in aqueous solution. Since both rate theory formulations utilize identical sets of molecular data, this provides a self-consistent theoretical picture of the rates of aqueous phase proton transfer. Specifically, we isolate and quantify the rates of proton transfer, ion-pair dissociation, and solvent exchange in concentrated HCl solutions. Our analysis predicts a concentration dependence to both proton transfer and ion-pairing. Moreover, our estimate of the lifetime for the Zundel species is 0.8 and 1.3 ps for 2 M and 8 M HCl, respectively. We demonstrate that concentration effects can indeed be quantified through the combination of state-of-the-art simulation and theory and provides a picture of the important correlations between the cation (hydronium) and the counterion in acid solutions.
速率理论通过提供一种物理透明的方法来分析动力学过程，在整个化学科学中都有很大的用途。在这里，我们展示了使用过渡态理论和 Marcus 理论来研究 HCl 溶液中质子转移速率的好处。通过使用长分子动力学模拟，我们表明这两种不同的速率理论形式之间存在很好的一致性，以及它们如何用于研究水溶液中质子转移的途径和寿命。由于这两种速率理论形式都使用了相同的分子数据集，这为水溶液中质子转移的速率提供了一个自洽的理论图景。具体来说，我们在浓 HCl 溶液中分离并量化了质子转移、离子对解离和溶剂交换的速率。我们的分析预测质子转移和离子配对都具有浓度依赖性。此外，我们对 Zundel 物种的寿命估计分别为 2 M 和 8 M HCl 中的 0.8 和 1.3 ps。我们证明，通过结合最先进的模拟和理论，确实可以量化浓度效应，并提供了酸溶液中阳离子（水合氢离子）和抗衡离子之间重要相关性的图景。
