Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk, 630090, Russia.
Novosibirsk State University, Novosibirsk, 630090, Russia.
Phys Rev E. 2017 Oct;96(4-1):042608. doi: 10.1103/PhysRevE.96.042608. Epub 2017 Oct 23.
Rayleigh-Brillouin light scattering is studied in liquid water over the range from 249 to 365 K. Experiments are carried out with a high spectral resolution (0.1 GHz), eliminating any contribution of the structural relaxation to the elastic line. The Landau-Placzek ratio is found as the ratio of the Rayleigh and Brillouin intensities. In the whole temperature range, the Landau-Placzek ratio is found to be in good agreement with a prediction of the theory with a pair of independent thermodynamic variables, pressure and entropy. This description is usually used for single-component homogeneous liquids. An excess of the Landau-Placzek ratio above the prediction is expected for inhomogeneous liquids and is observed, for example, in glass-forming liquids below a certain temperature. In contrast to glass-forming liquids, no excess of elastically scattered light increasing at low temperatures is observed for the Landau-Placzek ratio of water. This suggests that the Landau-Placzek ratio of liquid water can be described by a homogeneous structure, and the idea of the water structure consisting of two structural motifs may not be necessary to explain the experimental ratio.
瑞利-布里渊光散射在 249 到 365 K 的温度范围内的液态水中进行研究。实验采用高光谱分辨率（0.1GHz）进行，消除了结构弛豫对弹性线的任何贡献。朗道-普拉泽克比定义为瑞利和布里渊强度的比值。在整个温度范围内，朗道-普拉泽克比与理论预测值一致，该理论采用一对独立的热力学变量，即压力和熵。这种描述通常用于单相均匀液体。对于非均匀液体，预计朗道-普拉泽克比会超过预测值，例如在低于一定温度的玻璃形成液体中观察到。与玻璃形成液体不同，对于水的朗道-普拉泽克比，没有观察到低温下弹性散射光增加的过量。这表明液态水的朗道-普拉泽克比可以用均匀的结构来描述，并且可能不需要由两个结构基元组成的水结构的概念来解释实验比值。
