Smirnov Konstantin S
Univ. Lille, CNRS, UMR 8516 - LASIRe - Laboratoire Avancé de Spectroscopie pour les Interactions la Réactivité et l'Environnement, F-59000 Lille, France.
Molecules. 2024 Aug 8;29(16):3758. doi: 10.3390/molecules29163758.
Molecular dynamics simulations of model charged solid/water interfaces were carried out to provide insight about the relationship between the second-order nonlinear susceptibility χ(2) and the structure of the interfacial water layer. The results of the calculations reveal that the density fluctuations of water extend to about 12 Å from the surface regardless of the system, while the orientational ordering of molecules is long-ranged and is sensitive to the presence of electrolytes. The charge localization on the surface was found to affect only the high-frequency part of the Im[χ(2)] spectrum, and the addition of salt has very little effect on the spectrum of the first water layer. For solid/neat water interfaces, the spectroscopically active part of the liquid phase has a thickness largely exceeding the region of density fluctuations, and this long-ranged nonlinear activity is mediated by the electric field of the molecules. The electrolyte ions and their hydration shells act in a destructive way on the molecular field. This effect, combined with the screening of the surface charge by ions, drastically reduces the thickness of the spectroscopic diffuse layer. There is an electrolyte concentration at which the nonlinear response of the diffuse layer is suppressed and the χ(2) spectrum of the interface essentially coincides with that of the first water layer.
进行了模型带电固体/水界面的分子动力学模拟，以深入了解二阶非线性极化率χ(2)与界面水层结构之间的关系。计算结果表明，无论系统如何，水的密度涨落从表面延伸至约12 Å，而分子的取向有序是长程的，并且对电解质的存在敏感。发现表面上的电荷局域仅影响Im[χ(2)]光谱的高频部分，并且盐的添加对第一水层的光谱影响很小。对于固体/纯水界面，液相的光谱活性部分的厚度大大超过密度涨落区域，并且这种长程非线性活性由分子电场介导。电解质离子及其水合壳以破坏性方式作用于分子场。这种效应与离子对表面电荷的屏蔽相结合，极大地减小了光谱漫射层的厚度。存在一个电解质浓度，在该浓度下漫射层的非线性响应被抑制，并且界面的χ(2)光谱基本上与第一水层的光谱一致。
