非线性光学研究水及电解质水溶液界面——空气/电解质水溶液界面特定阴阳离子效应  

Nonlinear Optical Spectroscopy Studies on Water and Electrolyte Aqueous Solution Interfaces——Specific Ion Effect at Air/Electrolyte Aqueous Solution Interfaces

作　　者：邓罡华[1,2] 王鸿飞[2] 郭源[2] 

机构地区：[1]合肥微尺度物质科学国家实验室中国科学技术大学,合肥230026 [2]中国科学院化学研究所、北京分子科学国家实验室、分子反应动力学国家重点实验室,北京100190

出　　处：《化学进展》2012年第10期1865-1879,共15页Progress in Chemistry

基　　金：国家自然科学基金项目(No.20533070;21073199);中国科学院知识创新工程重要方向项目计划(No.KJCX-EW-W09)资助

摘　　要：水及电解质溶液界面在物理、化学、环境及生物等各种过程中扮演着至关重要的角色。百年来科学家用各种实验及理论方法研究水及电解质溶液界面,试图理解其界面的结构及动力学。最近的实验和理论研究表明离子能够影响电解质水溶液界面结构,可极化性大的阴离子甚至会在界面富集。本文综述了我们研究组近年来利用二阶非线性光学方法——非共振的二次谐波与和频振动光谱研究水及电解质溶液界面的进展。首先我们研究了空气/纯水界面非共振二次谐波信号的来源,研究结果证明了空气/纯水界面非共振二次谐波信号完全可以归结为电偶极贡献,为此方法在电解质溶液界面的研究奠定了基础。同时,用偏振及对称性分析对空气/纯水界面和频振动光谱峰进行了归属,提供了纯水/空气界面结构新的物理图像。在此基础上,我们对几种电解质水溶液界面进行了深入研究,结果证明不仅可极化性大的离子会在水界面富集,并使界面层增厚,可极化性小的阴离子对界面层厚度也有影响,甚至阳离子也会在一定程度上影响界面水分子结构。Water and electrolyte aqueous solution interfaces play crucial roles in many processes of physics, chemistry, environment, and biology. People have attempted to understand the structure and dynamics of water and electrolyte aqueous solution interfaces for decades. Recently, both experimental and theoretical studies have proved that larger and more polarizable anions attend to accumulate at the interface and affect the interfaeial water hydrogen bonding structure. In this review, we present recent progress of nonlinear optical spectroscopy studies on water and electrolyte aqueous solution interfaces with nonresonant second harmonic generation （SHG） and sum frequency generation vibrational spectroscopy （SFG-VS）. First, we addressed the signal source of the nonresonant second harmonic generation of the air/water interface. Analysis of the experimental results showed that the SHG signal of the air/water interface can be treated fully only with dipolar contribution, which lay the foundation of nonresonant second harmonic generation in studying water and electrolyte aqueous solution interfaces. We then utilized the polarization and molecular symmetry analyses to assign the SFG-VS spectra peaks to different interfacial species at the air/water interface. These results provide detailed informations on the orientation, structure, and dynamics of water molecules at the air/water interface. Subsequently, we studied several kinds of electrolyte aqueous solution interfaces by nonresonant SHG and SFG-VS. These results showed that not only the larger and more polarizable Branion, but also the smaller and less polarizable Cl-, F- anions are enriched at the air/water interface and increased the interfacial thickness. Furthermore, we also observed the specific Na^＋, K^＋ cation effect on the interfacial thickness and interfacial water hydrogen bonging structure.

关 键 词：水 电解质水溶液 界面 二次谐波 和频振动光谱 

分 类 号：O647.11[理学—物理化学] O645.17[理学—化学]