Laboratory for fundamental BioPhotonics (LBP), Institute of Bio-engineering (IBI), and Institute of Materials Science (IMX), School of Engineering (STI), and Lausanne Centre for Ultrafast Science (LACUS), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy.
J Phys Chem Lett. 2022 Aug 18;13(32):7462-7468. doi: 10.1021/acs.jpclett.2c01872. Epub 2022 Aug 5.
Water is the matrix of life and serves as a solvent for numerous physical and chemical processes. The origins of the nature of inhomogeneities that exist in liquid water and the time scales over which they occur remains an open question. Here, we report femtosecond elastic second harmonic scattering (fs-ESHS) of liquid water in comparison to an isotropic liquid (CCl) and show that water is indeed a nonuniform liquid. The coherent fs-ESHS intensity was interpreted, using molecular dynamics simulations, as arising from charge density fluctuations with enhanced nanoscale polarizabilities around transient voids having an average lifetime of 300 fs. Although voids were also present in CCl, they were not characterized by hydrogen bond defects and did not show strong polarizability fluctuations, leading to fs-ESHS of an isotropic liquid. The voids increased in number at higher temperatures above room temperature, in agreement with the fs-ESHS results.
水是生命的基质，也是众多物理和化学反应的溶剂。液体水中不均匀性的起源以及它们发生的时间尺度仍然是一个悬而未决的问题。在这里，我们报告了与各向同性液体（CCl）相比的液态水的飞秒弹性二次谐波散射（fs-ESHS），并表明水确实是一种不均匀的液体。使用分子动力学模拟对相干 fs-ESHS 强度进行了解释，认为其源自于具有增强的纳米级极化率的电荷密度波动，这些波动围绕具有平均寿命为 300fs 的瞬态空隙。尽管 CCl 中也存在空隙，但它们没有氢键缺陷的特征，也没有表现出强烈的极化率波动，这导致各向同性液体的 fs-ESHS。在室温以上的较高温度下，空隙的数量增加，这与 fs-ESHS 的结果一致。
