Department of Nanomaterial Science & Department of Chemistry, Chiba University, 1-33 Yayoi, Chiba 263-8522, Japan.
J Phys Chem B. 2012 Nov 26;116(46):13765-73. doi: 10.1021/jp307436t. Epub 2012 Nov 13.
We report here the low-frequency spectra, resulting from the intermolecular/interionic vibrational dynamics, of aqueous mixtures of an ionic liquid, 1-methyl-3-n-octylimidazolium tetrafluoroborate, with the H(2)O mole fractions of 0.2, 0.4, and 0.6 and the neat ionic liquid and H(2)O within the frequency range of 0.1-700 cm(-1) by means of femtosecond Raman-induced Kerr effect spectroscopy. Addition of H(2)O induces tiny effects on the line shape of the low-frequency Kerr spectrum of the ionic liquid: ca. a 2 cm(-1) red shift in the first moment of the low-frequency spectrum has been observed for a transition from the neat ionic liquid to the binary mixture containing 0.6 mol fraction of H(2)O. Surface tension and liquid density of the mixture also accompany minimal changes upon addition of H(2)O. These results suggest that H(2)O molecules localize at the interface between the ionic and nonpolar regions, and the interionic interaction in the ionic region is weakly perturbed by the existence of H(2)O. On the other hand, successive addition of H(2)O in the mixture slows down the picosecond overdamped relaxation process measured in the 3-300 ps range even though the shear viscosity of the mixture decreases substantially.
我们在此报告了在 0.1-700 cm(-1) 的频率范围内，通过飞秒 Raman 诱导克尔效应光谱法得到的，水与 1-甲基-3-正辛基咪唑四氟硼酸盐离子液体组成的混合体系（H(2)O 的摩尔分数分别为 0.2、0.4 和 0.6）中，由分子间/离子间振动动力学产生的低频谱。向离子液体中添加 H(2)O 会对低频 Kerr 光谱的线型产生微小影响：从纯离子液体到包含 0.6 摩尔分数 H(2)O 的二元混合物的转变，低频光谱的第一矩发生了约 2 cm(-1)的红移。混合物的表面张力和液体密度在添加 H(2)O 后也伴随着最小的变化。这些结果表明，H(2)O 分子定位于离子和非极性区域之间的界面处，并且离子区域中的离子相互作用受到 H(2)O 的存在的弱干扰。另一方面，尽管混合物的剪切粘度大幅下降，但在 3-300 ps 范围内测量的皮秒过阻尼弛豫过程中，H(2)O 的连续添加会使其变慢。
