Xu Man, Spinney Rick, Allen Heather C
Department of Chemistry, The Ohio State University, Columbus, 43210, USA.
J Phys Chem B. 2009 Apr 2;113(13):4102-10. doi: 10.1021/jp806565a.
The water surface structure of aqueous magnesium, calcium, and strontium nitrate solutions with six to seven water molecules on average solvating each ion was investigated using vibrational sum frequency generation (VSFG) spectroscopy. Raman (polarized) and infrared spectroscopies were used for understanding solvation effects. Infrared reflection spectra were analyzed to further understand the VSFG data. The VSFG spectral changes indicate that the divalent countercation species play a key role in the surface perturbation of the water. In addition, the data show that the solvated ions, and possibly their ion pairs, approach the aqueous surface. The identity of the divalent cation may cause a difference in the concentration gradient near the surface, thereby increasing the VSFG-active region, which then indicates an increase in the interfacial depth. The interface becomes thickened with Mg(2+) < Ca(2+) < Sr(2+). The free OH orientation measured from the surface normal from the salt solutions changes from 33 (from neat water) to approximately 60 degrees .
利用振动和频产生（VSFG）光谱研究了平均每个离子有六到七个水分子溶剂化的硝酸镁、硝酸钙和硝酸锶水溶液的水面结构。拉曼（偏振）光谱和红外光谱用于理解溶剂化效应。分析红外反射光谱以进一步理解VSFG数据。VSFG光谱变化表明二价抗衡阳离子物种在水的表面扰动中起关键作用。此外，数据表明溶剂化离子及其可能的离子对靠近水表面。二价阳离子的身份可能导致表面附近浓度梯度的差异，从而增加VSFG活性区域，进而表明界面深度增加。界面随着Mg(2+) < Ca(2+) < Sr(2+)而变厚。从盐溶液表面法线测量的游离OH取向从33（来自纯水）变为约60度。
