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arXiv 1507.06363cond-mat.softphysics.chem-ph
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水的氢键网络支持光学声子类模式的传播

The hydrogen bond network of water supports propagating optical phonon-like modes

Daniel C. Elton, M. -V. Fernández-Serra

摘要:

液态水的局部结构作为温度的函数是一个紧张的研究来源。这种结构与水分子的动力学密切相关,可以使用拉曼光谱和红外光谱进行测量。光谱峰的归属取决于它们是集体模式还是单分子运动。液体中的振动模式通常被认为与单个分子或小团簇的运动有关。利用分子动力学模拟,我们发现色散光学声子类模式的振动和OH伸缩带。我们认为,在亚皮秒的时间尺度上,这些模式通过水的氢键网络传播的距离高达两纳米。在长波长的限制,这些光学模式表现出横向分裂,表明存在相干的长程偶极-偶极相互作用,在冰。我们的研究结果表明,液态水的动力学与冰的相似之处比以前认为的要多。

英文摘要:

The local structure of liquid water as a function of temperature is a source of intense research. This structure is intimately linked to the dynamics of water molecules, which can be measured using Raman and infrared spectroscopies. The assignment of spectral peaks depends on whether they are collective modes or single molecule motions. Vibrational modes in liquids are usually considered to be associated to the motions of single molecules or small clusters. Using molecular dynamics simulations we find dispersive optical phonon-like modes in the librational and OH stretching bands. We argue that on subpicosecond time scales these modes propagate through water's hydrogen bond network over distances of up to two nanometers. In the long wavelength limit these optical modes exhibit longitudinal-transverse splitting, indicating the presence of coherent long range dipole-dipole interactions, as in ice. Our results indicate the dynamics of liquid water have more similarities to ice than previously thought.

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