Shirota Hideaki
Department of General Systems Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan.
J Chem Phys. 2005 Jan 22;122(4):44514. doi: 10.1063/1.1840420.
The ultrafast molecular dynamics of liquid aromatic molecules, benzene, toluene, ethylbenzene, cumene, and 1,3-diphenylpropane, and the mixtures with CCl(4) have been investigated by means of femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy. The picosecond Kerr transients of benzene, toluene, ethylbenzene, and cumene and the mixtures with CCl(4) show a biexponential feature. 1,3-Diphenylpropane and the mixtures with CCl(4) show triexponential picosecond Kerr transients. The slow relaxation time constants of the aromatic molecules and the mixtures with CCl(4) are qualitatively described by the Stoke-Einstein-Debye hydrodynamic model. The ultrafast dynamics have been discussed based on the Kerr spectra in the frequency range of 0-800 cm(-1) obtained by the Fourier transform analysis of the Kerr transients. The line shapes of the low-frequency intermolecular spectra located at 0-180 cm(-1) frequency range have been analyzed by two Brownian oscillators ( approximately 11 cm(-1) and approximately 45 cm(-1) peaks) and an antisymmetric Gaussian function ( approximately 65 cm(-1) peak). The spectrum shape of 1,3-diphenylpropane is quite different from the spectrum shapes of the other aromatic molecules for the low magnitude of the low-frequency mode of 1,3-diphenylpropane and/or an intramolecular vibration. Although the concentration dependences of the low- and intermediate-frequency intermolecular modes (Brownian oscillators) do not show a significant trend, the width of high-frequency intermolecular mode (antisymmetric Gaussian) becomes narrower with the higher CCl(4) concentration for all the aromatics mixtures with CCl(4). The result indicates that the inhomogeneity of the intermolecular vibrational mode in aromatics/CCl(4) mixtures is decreasing with the lower concentration of aromatics. The intramolecular vibrational modes of the aromatic molecules observed in the Kerr spectra are also shown with the calculation results based on the density functional theory.
利用飞秒光学外差检测拉曼诱导克尔效应光谱，研究了液态芳香分子（苯、甲苯、乙苯、异丙苯和1,3 - 二苯基丙烷）以及它们与四氯化碳混合物的超快分子动力学。苯、甲苯、乙苯和异丙苯及其与四氯化碳混合物的皮秒克尔瞬态呈现双指数特征。1,3 - 二苯基丙烷及其与四氯化碳的混合物呈现三指数皮秒克尔瞬态。芳香分子及其与四氯化碳混合物的慢弛豫时间常数可用斯托克斯 - 爱因斯坦 - 德拜流体动力学模型进行定性描述。基于通过克尔瞬态的傅里叶变换分析得到的0 - 800 cm⁻¹频率范围内的克尔光谱，讨论了超快动力学。位于0 - 180 cm⁻¹频率范围的低频分子间光谱的线形通过两个布朗振子（约11 cm⁻¹和约45 cm⁻¹峰）和一个反对称高斯函数（约65 cm⁻¹峰）进行了分析。由于1,3 - 二苯基丙烷低频模式的低强度和/或分子内振动，其光谱形状与其他芳香分子的光谱形状有很大不同。尽管低频和中频分子间模式（布朗振子）的浓度依赖性没有显示出明显趋势，但对于所有与四氯化碳的芳香族混合物，高频分子间模式（反对称高斯）的宽度随着四氯化碳浓度的增加而变窄。结果表明，随着芳香族化合物浓度降低，芳香族/四氯化碳混合物中分子间振动模式的不均匀性在减小。克尔光谱中观察到的芳香分子的分子内振动模式也与基于密度泛函理论的计算结果一起展示。
