利用超额拉曼光谱研究硝酸镁水溶液中的离子对.pdf

物理化学学报( Wuli Huaxue Xuebao)
August
Acta Phy.s.-Chim,Sin.2012,28(8),1823-1829
1823
Article
doi:10.3866/PKU.WHXB201205154
www.whxb.pku.edu.cn
利用超额拉曼光谱研究硝酸镁水溶液中的离子对
王陈琛林珂胡乃银周晓国刘世林”
(中国科学技术大学化学物理系,合肥微尺度物质科学国家实验室(筹)合肥230026)
摘要:利用超额拉曼光谱研究了室温下硝酸镁(Mg(NO)z)溶液的离子缔合情况.测量了该溶液羟基(一OH)伸
缩振动谱段和NO3全对称伸缩振动谱段的拉曼光谱,利用超额拉曼光谱及光谱拟合分析了这些光谱数据.一
OH伸缩振动谱段的超额拉曼光谱显示,低浓度(<2.3m?l~kg")下阴离子第一水合层的水分子含量随溶液浓度
的升高呈线性关系增加,在较高浓度时(>2.3mlkg~该含量变化偏离了线性关系,这是因为Mg(NO)2溶液
在高浓度时存在直接接触离子对导致的.同样的转折点浓度也在对NO全对称伸缩振动谱段的分析屮被观测
到.除了直接接触离子对,还观测到二种溶剂分隔型离子对.对该谱段下所有浓度的拉曼光谱和超额光谱进行
同时拟合,给出了不同浓度下各种离子对的相对含量,结果显示在0.23-4.86mlkg-'浓度范围内都有溶剂分
隔型离子对和直接接触型离子对.当Mg(NO3)2浓度低于2.3 molkg'时,所有离子对的相对含量随浓度增加呈
现直线上升,在高于这个浓度后直接接触离子对的相对含量急剧增加,一种溶剂分隔型离子对的相对含量增加
变缓,另一种溶剂分隔型离子对的相对含量逐渐减少,还有一种溶剂分隔型离子对相对含量的増加趋势保持不
变,在Mg(NO)2浓度大于3.5 molkg'后,其相对含量不再发生明显变化
关键词:硝酸镁水溶液;直接接触离子对;溶剂分隔离子对;超额拉曼光谱;同时拟合
中图分类号:O645
lon Pairs in Aqueous Magnesium Nitrate Solution by Excess
Raman Spectroscopy
WANG Chen-chen LIN Ke HU Nai-yin ZHOU Xiao-guo LIU Shi-lin
(Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and
Technology of China, Hefei 230026, P R. China)
Abstract: e study the ion associations in magnesium nitrate solution by Raman spectroscopy. Utilizing
the excess spectra and peak decomposition, we analyze the -OH stretching and NO] symmetric stretching
regions. Analysis of the - OH stretching region demonstrates that the amount of water molecules in the
first hydration shell of the anion follows a linear relationship in the low concentration range(<2.3 mol k.
but deviates from this linear relationship at high concentrations(2.3 mol kg ) The contact ion pairs at
high concentration result in the nonlinear variation n the NO symmetric stretching region, the contact ion
pairs and so vent separated ion pairs eist in the M(O) concentration region of.23-4.86 mol k
From a giobal fitting of the Raman spectra over the whole concentration region, we deduce that the
concentration of ion pairs aries. When the M(NO concen ration is below 2.3 mo. k, the relative
amounts of all ion pairs increase with the concentration. However, above this concentration, the relative
amount of contact ion pairs increases sharply, and solvent separated ion pairs either decrease or increase
in their lower rate, until the M(NO) concentration is 3.5 mol k", and above this concentration the
relative amount of one kind of solvent separated ion pair does not change
Received: April 1, 2012; Revised: May 14, 2012 Published on Web: May 15, 2012
Correspondingauthor.Email:slliu(@ustc.edu.cn;Tel:+86-551-3602323
The project was supported by the National Natural Science Foundation of China (21103158)and Specialized Research Fund for the Doctoral
Program of Higher Education, China (20103402110019)
国家自然科学基金(21103158)和高等学校博士学科点专项科研基金(20103402110019)资坳项目
C Editorial office ofacta Physico-chimica Sinica