A Fresh Perspective on Water Dynamics in Aqueous Salt Solutions

Abstract: Molecular dynamics in pure water and aqueous salt solutions remain incompletely understood, partly due to the apparent contradictions between results from different spectroscopic techniques. In this work, we demonstrate, by detailed comparison of light scattering and dielectric spectroscopy data for pure water and aqueous lithium chloride solutions, that these apparent contradictions can be resolved by accounting for orientational cross-correlations of neighboring molecules. Remarkably, a single structural relaxation mode with largely temperature- and concentration-independent shape can be identified in all spectra, from room temperature down to the deeply supercooled regime. These results provide a new perspective for the study of molecular dynamics in aqueous salt solutions.