X-RAY-ABSORPTION SPECTROSCOPY AND MOLECULAR-DYNAMICS STUDIES OF ZN2-SOLUTIONS( HYDRATION IN AQUEOUS)

The hydration of Zn2+ ions in aqueous solutions was studied at room te mperature by x-ray absorption spectroscopy and molecular dynamics (MD) simulation. The extended x-ray absorption fine structure (EXAFS) abov e the Zn K-edge was interpreted using the multiple-scattering approach by taking into account only one coordination Shell composed of 6 +/- 0.2 water molecules at R(Zn-O) = 2.06 +/- 0.02 Angstrom with a mean sq uare relative displacement (MSRD) sigma(2) = 0.009 +/- 0.002 Angstrom( 2). NO evidence-of significant contributions from the second hydration shell to the EXAFS signal was found in the solutions. This is explain ed by the cancellation interference effect between double-scattering a nd single-scattering EXAFS signals in the second shell due to large th ermal/static disorder (sigma(2) similar to 0.1 Angstrom(2)) as predict ed by our MD simulation and by known results of diffraction techniques .