title: The structure of water in the hydration shell of cations from x-ray Raman and small angle x-ray scattering measurements.
abstract: X-ray Raman scattering (XRS) spectroscopy and small angle x-ray scattering (SAXS) are used to study water in aqueous solutions of NaCl, MgCl(2), and AlCl(3) with the particular aim to provide information about the structure of the hydration shells of the cations. The XRS spectra show that Na(+) weakens the hydrogen bonds of water molecules in its vicinity, similar to the effect of increased temperature and pressure. Mg(2+) and Al(3+), on the other hand, cause the formation of short and strong hydrogen bonds between the surrounding water molecules. The SAXS data show that Mg(2+) and Al(3+) form tightly bound hydration shells that give a large density contrast in the scattering data. From the form factors extracted from the SAXS data, we found that Mg(2+) and Al(3+) have, respectively, an equivalent of one and one and a half stable hydration shells that appear as a density contrast. In addition, we estimated that the density of water in the hydration shells of Mg(2+) and Al(3+) is, respectively, ∼61% and ∼71% higher than in bulk water.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California 94305, USA.
authors.forename: Iradwikanari
authors.initials: I
authors.lastname: Waluyo
authors.forename: Congcong
authors.initials: C
authors.lastname: Huang
authors.forename: Dennis
authors.initials: D
authors.lastname: Nordlund
authors.forename: Uwe
authors.initials: U
authors.lastname: Bergmann
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Weiss
authors.forename: Lars G M
authors.initials: LG
authors.lastname: Pettersson
authors.forename: Anders
authors.initials: A
authors.lastname: Nilsson
mesh_terms: D000077410:Aluminum Chloride; D017607:Aluminum Compounds / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry*; D006860:Hydrogen Bonding; D015636:Magnesium Chloride / Q000737:chemistry*; D015394:Molecular Structure; D053838:Scattering, Small Angle; D012965:Sodium Chloride / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D017607:Aluminum Compounds; D002412:Cations; D002712:Chlorides; D015636:Magnesium Chloride; D014867:Water; D000077410:Aluminum Chloride; D012965:Sodium Chloride