Hydration of Alkali Metal and Halide Ions from Static and Dynamic Viewpoints

Ionhydration in aqueous solutions plays a paramount role in manyfields. Despite many studies on ion hydration, the nature of ion hydrationis not consistently understood at the molecular level. Combining neutronscattering (NS), wide-angle X-ray scattering (WAXS), and moleculardynamics (MD), we quantify the ionic hydration degree (hydration ability)systematically for a series of alkali metal and halide ions basedon static and dynamic hydration numbers. The former is based on theorientational correlation of water molecules bound to an ion derivedfrom the positional information from NS and WAXS. The latter is definedas the mean number of water molecules remaining in the first coordinationshell of an ion over a residence time of bound water molecules aroundthe ion from MD. The static and dynamic hydration numbers distinguishhydration from coordination and quantify the ionic hydration degree,which provides a valuable reference for understanding various phenomenain nature.