Abstract: Aqueous structures with salt to water molar ratios of 1:30 (Rb2SO4) and 1:14 (Cs2SO4) were measured by X-ray scattering of synchrotron radiation. The radial distribution functions (RDF) of the two example solutions were obtained by analyzing the scattering data. RDF overlapped peaks near the first hydration shell were dealt with Gaussian multi-peak fitting. The fitting data were agreed well with the experimental data. The adscription of every fitting peak was determined by comparing the fitting data with hydrated ion and crystal structure data reported in literatures. The analysis of fitting result indicates that the coordination number of Rb+ and Cs+ is six in the first hydration shell, and the spatial structures are both distorted octahedrons. The contact ion pairs of metal ions with sulphate ion exist in two solutions where the characteristic distances of Rb—S and Cs—S were determined to be 0.407 and 0.427 nm, respectively. The study demonstrated that multi-peak fitting was useful for interpreting the hydrated structure of ions.

Key words: Synchrotron radiation, X-ray scattering, Radial distribution function, Multi-peak fitting, Hydrated structure