Ion solvation under gigapascal pressure

Jing, Z.*; Yamaguchi, Toshio*; Machida, Shinichi*; Hattori, Takanori   ; Zhou, Y.*

Ion solvation in a range of gigapascal pressure is of great significance for high-pressure chemical synthesis and the circulation of matter within the Earth's interior. We perform neutron scattering (NS) experiments and molecular dynamics simulations of deuterated aqueous solutions of MCl (M = Li, Na, K, Rb, and Cs) at 0.1 MPa and 0.7 GPa/298 K. An empirical potential structure refinement method analyzes the NS data. Upon compression to 0.7 GPa, the outer-shell water molecules enter the nearest neighbor of ions, and the solvated ion clusters become denser. The hydration factor and static hydration number based on the orientation distribution of the water dipole in the first solvation shell, show that the compression weakens the hydration ability of the ions. Compression suppresses the diffusion of ions, particularly of the structure-breaking ions. The ionic diffusion coefficient residence time of water molecules and dynamic hydration number indicate that Rb and Cs exhibit characteristics of structure-making ions under compression. The dynamic properties are more pressure-sensitive than the static structure.