Cappa Christopher D, Smith Jared D, Wilson Kevin R, Messer Benjamin M, Gilles Mary K, Cohen Ronald C, Saykally Richard J
Department of Chemistry, University of California and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460, USA.
J Phys Chem B. 2005 Apr 21;109(15):7046-52. doi: 10.1021/jp0445324.
Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions demonstrate that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS, analogous to those observed when increasing the temperature of pure water. The main-edge feature exhibits unique behavior and becomes more intense when salt is added. Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations, which result primarily from intensity changes of specific transitions due to geometric rearrangement of the hydrogen bond network.
对卤化钠水溶液的氧 K 边 X 射线吸收光谱（XAS）测量表明，离子会显著扰乱相邻水分子的电子结构。向水中添加卤化物盐会导致 XAS 的前缘强度增加而后缘强度降低，这与升高纯水温度时观察到的情况类似。主边缘特征表现出独特的行为，添加盐时会变得更强。XAS 的密度泛函理论计算表明，观察到的水跃迁随盐浓度的红移源于阴离子对水上未占据分子轨道的强烈直接扰动，并且不需要第一溶剂化层之外的氢键网络发生显著变形。这与温度依赖的光谱变化形成对比，后者主要是由于氢键网络的几何重排导致特定跃迁强度变化引起的。
