β胡萝卜素是典型的线性多稀分子, 重要的光电材料, 在医学上也有重要的作用, 研究它在外场作用下分子结构和性能的变化及机理有很重要的理论和应用价值。 分别测量了β胡萝卜素在二甲基亚砜中温度为81～25 ℃范围和β胡萝卜素在二硫化碳中压力为0.04～0.60 GPa范围的紫外-可见吸收和共振拉曼光谱。 发现了两种不同的的光谱现象, 随温度降低, 二甲基亚砜中的β胡萝卜素分子的紫外-可见吸收、 拉曼光谱都红移, 拉曼散射截面增大; 而随压强增加二硫化碳中β胡萝卜素分子的紫外-可见吸收峰也红移, 但拉曼散射峰却蓝移, 拉曼散射截面减小。 两种实验现象不能同时用线性多烯分子的“有效共轭长度”“弱阻尼相干振动”等理论模型给予明了解释。 电子—声子耦合常数, 可以表征分子中的原子和电子在外界环境作用下的相互振动耦合程度的强弱。 该研究依据电子—振动相互作用规律, 通过分析和计算得出结论: 二种实验现象都是π电子与碳碳键振动相互作用产生的, 即由于温度、 压力作用对β胡萝卜素分子结构及电子—振动耦合影响不同, 引起电子-声子耦合常数不同, 是电子能隙对碳碳振动的调制作用而产生的两种实验结果。

The Visible absorption and Raman spectra of β-carotene were measured in dimethyl sulfoxide in temperature ranging from 81 to 25 ℃ and in carbon disulfide in pressure range from 0.04 to 0.60 GPa, respectively. The results indicated that the visible absorption and Raman spectra are both red-shifted, Raman scattering cross section increase with the temperature decreasing. And with the pressure increasing, the visible absorption spectra are red-shifted, but the frequency shift towards higher frequencies in the Raman spectra, the Raman scattering cross section decrease unexpectedly. The latter can’t be explained by the model of “effective conjugation length” and “coherent weakly damped electron-lattice vibrations”. In this paper, we combined electron-vibration coupling rule with theoretical calculations and found that the electron-phonon coupling constant had a certain changing trend with the temperature and pressure variation, which Indicate that the interaction between π-electron and CC bond vibration was essential for this experiment result. Thus, the turning effect of energy gap of the π on CC vibration mode is responsible for such phenomenon.