Department of Chemistry, Stanford University, Stanford, California 94305, USA.
J Chem Phys. 2011 Jun 14;134(22):224507. doi: 10.1063/1.3597606.
X-ray absorption spectroscopy (XAS) and small angle x-ray scattering (SAXS) were utilized to study the effect of fluoride (F(-)) anion in aqueous solutions. XAS spectra show that F(-) increases the number of strong H-bonds, likely between F(-) and water in the first hydration shell. SAXS data show a low-Q scattering intensity increase similar to the effect of a temperature decrease, suggesting an enhanced anomalous scattering behavior in F(-) solutions. Quantitative analysis revealed that fluoride solutions have larger correlation lengths than chloride solutions with the same cations but shorter compared to pure water. This is interpreted as an increased fraction of tetrahedral low-density structures in the solutions due to the presence of the F(-) ions, which act as nucleation centers replacing water in the H-bonding network and forming stronger H-bonds, but the presence of the cations restricts the extension of strong H-bonds.
X 射线吸收光谱（XAS）和小角 X 射线散射（SAXS）被用于研究氟离子（F(-)）在水溶液中的影响。XAS 光谱表明 F(-)增加了强氢键的数量，可能是在第一水合壳层中 F(-)与水之间形成的。SAXS 数据显示低-Q 散射强度增加类似于温度降低的效果，表明 F(-)溶液中增强的异常散射行为。定量分析表明，与具有相同阳离子的氯化物溶液相比，氟化物溶液具有更大的相关长度，但与纯水相比更短。这被解释为由于 F(-)离子的存在，溶液中具有更多的四面体低密度结构，F(-)离子充当成核中心，取代氢键网络中的水并形成更强的氢键，但阳离子的存在限制了强氢键的延伸。
