Department of Chemistry, School of Education, Shizuoka University, Ohya, Shizuoka, Japan.
J Phys Chem B. 2011 May 26;115(20):6636-43. doi: 10.1021/jp201695b. Epub 2011 May 4.
The modulations in the electron density induced by molecular motions are analyzed theoretically for tetrahedrally hydrogen-bonded water molecules. Those modulations are represented as the electron density derivatives, and their forms are examined by the use of the one- and two-dimensional integrated plots. It is shown that intermolecular flux of electrons, called intermolecular charge flux, is induced by the molecular translation modes in water, leading to the infrared intensity at 6 THz. This means that the molecular translational and electronic motions are strongly coupled, and this coupling is observable through this vibrational band. A comparison is made with the case of the OH stretching mode. A method to incorporate this effect in spectral simulations based on classical molecular dynamics is also shown. These results provide a way to correct understanding of dynamics in, for example, aqueous solutions of biomolecules from analyses of their vibrational spectra in the terahertz frequency region. A general idea on how we can perform reasonable calculations and analyses of the vibrational spectral profiles of liquid systems is also discussed.
对具有四面体氢键的水分子，从理论上分析了分子运动引起的电子密度调制。这些调制被表示为电子密度导数，并通过使用一维和二维积分图来检查它们的形式。结果表明，电子的分子间流动，即分子间电荷流动，是由水分子的平移模式引起的，导致在 6 THz 处出现红外强度。这意味着分子平移和电子运动强烈耦合，这种耦合可以通过这个振动带观察到。与 OH 伸缩模式的情况进行了比较。还展示了一种基于经典分子动力学的光谱模拟中纳入这种效应的方法。这些结果为从太赫兹频率区域的振动光谱分析中，例如，从生物分子在水溶液中的动力学提供了一种校正理解的方法。还讨论了关于如何对液体系统的振动光谱轮廓进行合理计算和分析的一般思路。
