Real-space Dynamics in Aqueous Salt Solution

We report on the real-space correlated motion of water molecules and ions in an aqueous salt solution. The Van Hove functions–pair-correlation functions in space and time–of aqueous salt solution were determined by high-resolution inelastic X-ray scattering (IXS) spectra over a wide range of momentum transfer and energy transfer as well as molecular dynamics simulation. (Pseudo-) Partial Van Hove function was determined to disentangle the element-specific correlated motions. Our results directly depict the distance-dependent correlated dynamics of aqueous salt solutions in picosecond timescale and identify the changes in the anion–water and cation–water correlations. We found that the ion–water correlations show a two-step relaxation, which corresponds to a local rattling-like vibration and the local configurational rearrangement.