Wang Shuzhi, Bianco Roberto, Hynes James T
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA.
J Phys Chem A. 2009 Feb 19;113(7):1295-307. doi: 10.1021/jp808533y.
The acid dissociation of a nitric acid HNO(3) molecule located at various depths in a water slab is investigated via Car-Parrinello molecular dynamics simulations. HNO(3) is found to remain molecular when it is adsorbed on top of the surface with two hydrogen-bonds, and to dissociate--although not always--by transferring a proton to a water molecule within a few picoseconds when embedded at various depths within the aqueous layer. The acid dissociation events are analyzed and discussed in terms of the proton donor-acceptor O-O hydrogen bonding distance and the configurations of the nearest-neighbor solvent waters of an HNO(3).H(2)O pair. Four key structural features for the HNO(3) acid dissociation are identified and employed to analyze the trajectory results. Key solvent motions for the dissociation include the decrease of the proton donor-acceptor O-O hydrogen bonding distance and a 4 to 3 coordination number change for the proton-accepting water. The Eigen cation (H(3)O(+)), rather than the Zundel cation (H(5)O(2)(+)), is found to be predominant next to the NO(3)(-) ion in contact ion pairs in all cases.
通过Car-Parrinello分子动力学模拟研究了位于水板不同深度处的硝酸HNO₃分子的酸解离。发现HNO₃通过两个氢键吸附在表面顶部时保持分子状态，而当嵌入水层内的不同深度时，它会在几皮秒内通过将质子转移到水分子上而解离——尽管并非总是如此。根据质子供体-受体O-O氢键距离以及HNO₃·H₂O对的近邻溶剂水分子的构型对酸解离事件进行了分析和讨论。确定了HNO₃酸解离的四个关键结构特征，并用于分析轨迹结果。解离的关键溶剂运动包括质子供体-受体O-O氢键距离的减小以及质子接受水分子的配位数从4变为3。在所有情况下，发现Eigen阳离子（H₃O⁺）而非Zundel阳离子（H₅O₂⁺）在接触离子对中紧邻NO₃⁻离子时占主导地位。
