物理化学学报 >> 2010, Vol. 26 >> Issue (04): 964-970.doi: 10.3866/PKU.WHXB20100418

光化学与光谱 上一篇    下一篇

飞秒光学外差光学克尔效应和低频拉曼光谱技术研究离子液体[bmim][PF6]的低频光谱

王维, 吕荣, 于安池   

  1. 中国人民大学化学系, 北京 100872
  • 收稿日期:2009-12-29 修回日期:2010-01-21 发布日期:2010-04-02
  • 通讯作者: 于安池 E-mail:a.yu@chem.ruc.edu.cn

Low Frequency Spectrumof Ionic Liquid [bmim][PF6] Studied by Femtosecond Optically Heterodyne-Detected Optical Kerr Effect Spectroscopy and Low Frequency Raman Spectroscopy

WANG Wei, LV Rong, YU An-Chi   

  1. Department of Chemistry, Renmin University of China, Beijing 100872, P. R. China
  • Received:2009-12-29 Revised:2010-01-21 Published:2010-04-02
  • Contact: YU An-Chi E-mail:a.yu@chem.ruc.edu.cn

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摘要：

利用飞秒光学外差光学克尔效应技术获得了咪唑类离子液体1-丁基-3-甲基咪唑六氟磷酸盐([bmim][PF6])体系中反映分子间相互作用的低频光谱. 结果分析中, 利用Brownian振子时间相关函数的精确表达式对光学克尔效应动力学数据中的核振动部分进行模拟, 在时域上获得各个振动组分的时间演化行为, 并进而通过快速Fourier变换获得各个振动组分的频域光谱和总加和光谱. 此外还利用低频拉曼光谱技术测量了离子液体[bmim][PF6]的低频光谱, 并和飞秒光学外差光学克尔效应实验的结果进行对比, 发现两种方法获得的低频光谱相近. 实验结果表明Brownian振子时间相关函数的精确表达式可用来解析离子液体体系中低频振动的时间演化行为.

关键词: 低频拉曼光谱, 飞秒光学外差光学克尔效应, 离子液体, [bmim][PF6], 低频振动, Brownian振子

Abstract:

The low frequency vibrational spectrum that reflects the intermolecular interaction of an imidazolium cation ionic liquid 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF6]) was studied by femtosecond optically heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy. Several explicit time correlation functions of the Brownian oscillator were used to simulate the kinetic nuclear contribution of the femtosecond OHD-OKE data. The time evolution behavior of each individual oscillator in the time domain was obtained. We obtained the frequency spectrum for each oscillator in the frequency domain by the fast Fourier transform theorem. In addition, we also measured the low frequency vibrational spectrum of [bmim][PF6] by low frequency Raman spectroscopy. These low frequency spectra obtained by low frequency Raman spectroscopy and by femtosecond OHD-OKE spectroscopy show very similar characteristics. These results demonstrate that the explicit time correlation function of the Brownian oscillator can be used to resolve the time evolution behavior of the low frequency vibration mode in ionic liquids.

Key words: Low frequency Raman spectroscopy, Femtosecond optically heterodyne-detected optical Kerr effect, Ionic liquid, [bmim][PF6], Low frequency vibration, Brownian oscillator