盐对甲醇微观结构的影响

利用拉曼光谱研究盐对甲醇微观结构的影响.比较了不同盐/甲醇体系的O—H伸缩谱段和C—O伸缩谱段的超额拉曼光谱,对比给出了阴、阳离子与甲醇的相互作用.O—H伸缩谱段的超额拉曼光谱明显地显示了阴离子与甲醇形成弱氢键,氢键强度排序为CH3OH-CH3OHCl--CH3OHNO3--CH3OHClO4--CH3OH,在这个波段内,基本观察不到阳离子与甲醇的相互作用.在C—O伸缩谱段内,阴阳离子均有显著的体现,且与它们作用的甲醇C—O伸缩振动频率有如下的关系:CH3—OH(阴离子)CH3—OH(体相)CH3—OH(阳离子).根据C—O伸缩谱段的超额拉曼光谱,拟合了该谱段的拉曼光谱,由分解的谱峰强度得到阴、阳离子第一溶剂化层中甲醇分子的数目,结果显示在该浓度(～0.005)下离子对第一溶剂化层以外的甲醇氢键网络结构没有明显影响.

Effects of Salts on the Microstructure of Methanol

We studied the effects of salts on the microstructure of liquid methanol using the Raman spectra. We compared the excess Raman spectra of different methanolic salt solutions in the O—H and C—O stretching regions. These regions reflect the interactions between anions (cations) and methanol molecules. In the O—H stretching region, the excess spectra show that the anions interact with methanol molecules by weak hydrogen bonding and the strength of the hydrogen bonds decrease according to the order: CH₃OH-CH₃OH>Cl--CH₃OH>NO- ₃ -CH₃OH>ClO- ₃ -CH₃OH. Additionally, no interactions between cations and methanol molecules are apparent, as determined after analysis of this region. In the C—O stretching region, the excess Raman spectra show the interactions between anions (cations) and methanol molecules. The C—O stretching vibration frequencies of methanol that interact with the anions and cations increase according to the order: CH₃—OH (anions)3—OH (bulk)3—OH (cations). According to the excess Raman spectra in the C—O stretching region, we fitted the Raman spectra and used the fitting results to determine the solvation numbers in the first solvation shell of the ions. The Raman spectra show that the ions do not affect the microstructure of liquid methanol beyond the first solvation shell at this concentration (~0.005).