X-ray absorption spectroscopy and molecular dynamics studies of hydration in aqueous solutions

The hydration of ions in aqueous solutions was studied at room temperature by x-ray absorption spectroscopy and molecular dynamics (MD) simulation. The extended x-ray absorption fine structure (EXAFS) above the Zn K-edge was interpreted using the multiple-scattering approach by taking into account only one coordination shell composed of water molecules at R(Zn - O) = with a mean square relative displacement (MSRD) . No evidence of significant contributions from the second hydration shell to the EXAFS signal was found in the solutions. This is explained by the cancellation interference effect between double-scattering and single-scattering EXAFS signals in the second shell due to large thermal/static disorder as predicted by our MD simulation and by known results of diffraction techniques.