Protons in supercritical water: a multistate empirical valence bond study.
Protons in supercritical water: a multistate empirical valence bond study.
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超临界水中的质子：多态经验价键研究。
DOI：
10.1021/ja0373418
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发表时间：
2004
影响因子：
15
通讯作者：
E. Guàrdia
中科院分区：
文献类型：
--
作者：
D. Laria;J. Martí;E. Guàrdia
我们进行了分子动力学模拟，以分析与沿超临界 T = 673 K 等温线过量质子水溶剂化相关的微观细节，跨越从典型液体到蒸汽环境的密度区间。模拟方法依赖于包含质子易位机制的多态经验价键哈密顿模型。我们的结果预测溶剂化本征阳离子 [H(3)O.(H(2)O)(3)](+) 在较低密度下逐渐稳定，不利于对称 Zundel 二聚体 [H.(H(2)O)(2)](+)。在所有密度下，水合氢附近的平均溶剂化结构的特征是三个氢键受体水分子，并且溶质水距离呈现微小变化。质子易位跳跃的特征时间已经使用群体弛豫时间相关函数计算出来。与室温结果相比，高密度下的速率快 4 倍，并且在类似蒸汽的环境中逐渐变慢。还计算了过量质子的扩散系数。与电导数据一致，我们的结果表明，格罗特斯机制对整体质子传输的贡献在较低密度下减少，并预测在类蒸汽环境中，质子扩散几乎比纯水慢 1 个数量级。溶剂化质子的光谱信息与低密度下本征样结构中质子局域化的逐渐普遍一致。
Molecular dynamics simulations have been performed to analyze microscopic details related to aqueous solvation of excess protons along the supercritical T = 673 K isotherm, spanning a density interval from a typical liquid down to vapor environments. The simulation methodology relies on a multistate empirical valence bond Hamiltonian model that includes a proton translocation mechanism. Our results predict a gradual stabilization of the solvated Eigen cation [H(3)O.(H(2)O)(3)](+) at lower densities, in detriment of the symmetric Zundel dimer [H.(H(2)O)(2)](+). At all densities, the average solvation structure in the close vicinity of the hydronium is characterized by three hydrogen bond acceptor water molecules and presents minor changes in the solute water distances. Characteristic times for the proton translocation jumps have been computed using population relaxation time correlation functions. Compared to room temperature results, the rates at high densities are 4 times faster and become progressively slower in steamlike environments. Diffusion coefficients for the excess proton have also been computed. In agreement with conductometric data, our results show that contributions from the Grotthus mechanism to the overall proton transport diminish at lower densities and predict that in steamlike environments, the proton diffusion is almost 1 order of magnitude slower than that for pure water. Spectroscopic information for the solvated proton is accordant to the gradual prevalence of proton localization in Eigen-like structures at lower densities.