正烷烃分子的太赫兹频段振动动力学

The vibrational dynamics of n-alkanes in the terahertz region

本文应用太赫兹时域光谱技术研究了C5–C10,C18,C22,C32正烷烃在太赫兹频段的光学特性,在C5–C10范围内,正烷烃的折射率随着碳链的增长而单调线性递增,在C18–C32范围内,折射率值出现拐点后与碳数成线性递增关系,而吸收系数与碳数及表面形貌之间没有明显直接的关系.结合密度泛函理论计算得到了C5–C10,C18正烷烃在太赫兹频段的振动谱,正烷烃在太赫兹频段的主要吸收模式来源为C-C链大骨架振动,并且分子大骨架振动的频率随着碳数的增加向低频移动.实验结果为石油有机质的太赫兹光谱分析提供了理论基础,表明太赫兹技术可以用于烷烃分子物理性质的预测分析.

Much attention has been paid to the studies on the dynamics of n-alkanes, which is also the key physical problems exist in the rapid identification of crude oil or the database establishment for hundreds of petroleum products. In this paper, the optical properties of C5–C10, C18, C22 and C32 n-alkanes were investigated using terahertz time-domain spectroscopy. The refractive index of C5-C10 n-alkanes is found to vary linearly with chain length. The refractive index of C18 n-alkane encountered inflection point, and then vary linearly with chain length in the range of C18–C32. The absorption coefficients of n-alkanes has no significant direct relationship with carbon numbers and surface topography. In order to further understand the absorption spectra, combined with density functional theory, the vibrational spectroscopy of C5–C10 and C18 n-alkanes were calculated in the terahertz region using GAUSSIAN 03 software package. The B3 LYP method was used in conjunction with the 6–31 G basis set. The vibration of C-C chain skeleton is the main absorption model of n-alkanes in the terahertz range. The vibrational frequency of C-C chain skeleton is moved toward the low frequency when the carbon numbers increased. The results provided a theoretical basis for terahertz analysis of petroleum and organic compounds, and indicated that terahertz technology can be used for the physical properties prediction of n-alkanes.