构建时间分辨相干反斯托克斯拉曼散射(CARS)光谱系统,从微观层次研究硝基甲烷的分子相干振动动力学特性.实验中采用超连续白光作为斯托克斯光,通过调整斯托克斯光的时间延迟,得到不同振动模式的CARS光谱.通过对振动弛豫曲线的拟合,获得硝基甲烷分子不同振动模式的振动失相时间.结果表明C—H键伸缩振动比C—N键伸缩振动更容易受热声子的影响.在热加载下,硝基甲烷分子的C—H键有望首先被激发并引起初始化学反应.%The initial decomposition micro-mechanism of energetic materials has attracted much attention because it is a critical factor for the safe use of energetic materials. The thermally triggered chemical reactions are usually related to the vibrational properties of molecules. A time-resolved coherent anti-Stokes Raman scattering(CARS)spectrum system is constructed to study the molecular coherent vibrational dynamics of nitromethane at a microscopic level for clarifying the relation of molecular vibration to initial chemical reaction. In this experiment, the ultra-continuous white light is used as Stokes light,and the CARS spectra of different vibrational modes can be obtained by adjusting the time delay of the Stokes light. The vibrational dephasing time of different chemical bonds in nitromethane is provided by fitting the vibrational relaxation curves. The dephasing time of the C—H stretching vibration located at 3000 cm?1is shown to be 0.18 ps, which is far less than the dephasing time 6.2 ps of the C—N stretching vibration located at 917 cm?1. The vibrational dephasing time is closely related to thermal collision for liquid nitromethane system without intermolecular hydrogen bond, that is, the scattering of thermal phonons causes the dephasing of coherent vibration. Therefore, the stretching vibration of the C—H bond is more easily affected by the thermal phonon than the stretching vibration of the C—N bond. The C—H bond of nitromethane molecule is expected to be excited first, causing an initial chemical reaction under thermal loading.
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