Xue Lianjie, Bardak Fehmi, Tamas George, Quitevis Edward L
Department of Chemistry & Biochemistry, Texas Tech University, Lubbock, TX 79409, USA.
Phys Chem Chem Phys. 2017 Feb 8;19(6):4661-4672. doi: 10.1039/c6cp08263g.
This article describes a comparative study of the low-frequency (0-450 cm) Kerr spectra of the branched 1-(iso-alkyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([(N - 2)mCCim][NTf] with N = 3-7) ionic liquids (ILs) and that of the linear 1-(n-alkyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([CCim][NTf] with N = 2-7) ILs. The spectra were obtained by use of femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The intermolecular spectrum of a branched IL is similar to that of a linear IL that is of the same alkyl chain length rather than of the same number of carbon atoms in the alkyl chain. This similarity and the lack of a correlation of the first spectral moments and widths of the intermolecular spectra with chain length is mainly attributed to the increase in the dispersion contribution to the total molar cohesive energy being compensated by stretching of the ionic network due to the increasing size of the nonpolar domains, which is dependent only on the length of the alkyl chain.
本文描述了支链型1-(异烷基)-3-甲基咪唑双(三氟甲基磺酰)亚胺（[(N - 2)mCCim][NTf]，N = 3 - 7）离子液体（ILs）与直链型1-(正烷基)-3-甲基咪唑双(三氟甲基磺酰)亚胺（[CCim][NTf]，N = 2 - 7）离子液体在低频（0 - 450厘米）克尔光谱方面的比较研究。这些光谱是通过飞秒光学外差检测拉曼诱导克尔效应光谱法（OHD - RIKES）获得的。支链离子液体的分子间光谱与具有相同烷基链长度而非相同烷基链中碳原子数的直链离子液体的分子间光谱相似。这种相似性以及分子间光谱的第一光谱矩和宽度与链长度缺乏相关性，主要归因于随着非极性域尺寸的增加，离子网络的拉伸对总摩尔内聚能的色散贡献增加得到了补偿，而非极性域尺寸仅取决于烷基链的长度。
