Borgis Daniel, Belloni Luc, Levesque Maximilien
Maison de la Simulation , USR 3441 CNRS-CEA-Université Paris-Saclay , 91191 Gif-sur-Yvette , France.
PASTEUR, Département de Chimie, École Normale Supérieure , PSL University, Sorbonne Université, CNRS , 75005 Paris , France.
J Phys Chem Lett. 2018 Jul 5;9(13):3698-3702. doi: 10.1021/acs.jpclett.8b01690. Epub 2018 Jun 22.
We derive a theoretical expression of the second harmonic scattering signal in diluted electrolytes compared with bulk water. We show that the enhancement of the signal with respect to pure water observed recently for electrolytes at very low dilution in the micromolar range is a mere manifestation of the Debye screening that makes the infinite-range dipole-dipole solvent correlations in 1/ r disappear as soon as the ionic concentration becomes finite. In q space, this translates into a correlation function having a well known singular behavior around q = 0, which drives the observed ionic effects. We find that the signal is independent of the ion-induced long-range behavior of the function ⟨cos ϕ( r)⟩ that has been recently discussed. We find also that the enhancement depends on the experimental geometry and occurs only for in-plane polarization detection, as observed experimentally. On the contrary, the measured isotope effect between light and heavy water cannot be fully explained.
我们推导了与本体水相比，稀电解质中二次谐波散射信号的理论表达式。我们表明，最近在微摩尔范围内极低稀释度的电解质中观察到的相对于纯水信号的增强，仅仅是德拜屏蔽的一种表现，一旦离子浓度变为有限值，它就会使1/r中无限范围的偶极 - 偶极溶剂相关性消失。在q空间中，这转化为相关函数在q = 0附近具有众所周知的奇异行为，这驱动了观察到的离子效应。我们发现信号与最近讨论的函数〈cos ϕ(r)〉的离子诱导长程行为无关。我们还发现，如实验观察到的那样，增强取决于实验几何结构，并且仅发生在面内偏振检测中。相反，轻水和重水之间测得的同位素效应无法得到充分解释。
