A different view of structure-making and structure-breaking in alkali halide aqueous solutions through x-ray absorption spectroscopy

作者：Waluyo Iradwikanari; Nordlund Dennis; Bergmann Uwe; Schlesinger Daniel; Pettersson Lars G M; Nilsson Anders^*

来源：Journal of Chemical Physics, 2014, 140(24): 244506.

DOI：10.1063/1.4881600

X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl- and Br- are shown to have insignificant effect on the structure of water while I-locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na+ and the effect on the liquid as similar to an increase in temperature.

• 出版日期2014-6-28