共振拉曼效应和电子-声子耦合对线性多烯分子共振拉曼光谱的影响

线性多烯分子具有高强度且信息丰富的共振拉曼光谱，在生物学、光电材料和医学等方面都有一定应用。而含有共轭双键的短链β胡萝卜素分子是多烯分子中极具有代表性的分子。在激发光作用下π电子与CC键振动相互作用影响着吸收光谱和拉曼光谱，而共振拉曼效应和电子-声子耦合影响着共振拉曼光谱的强度、频率和线型。测量了β胡罗卜素分子在二氯乙烷中283～223 K温度范围内的紫外-可见吸收和共振拉曼光谱。研究了共振效应和电子-声子耦合对吸收光谱和拉曼光谱的变化所起的作用。获得随着温度的降低，黄昆因子减小，表明CC键的振动减弱，分子体系能量减小，吸收峰红移；随着温度的降低，分子有序性提高，电子-声子耦合强度增加，增强了电子能隙对CC键振动的调制作用，拉曼模频率向低波数方向移动，即拉曼光谱红移；同时，经过计算发现随着温度的降低，β胡萝卜素分子C-C和C═C的拉曼散射截面增加，线宽变窄，倍频与基频强度比增加。对比和分析了共振效应和电子-声子耦合作用对拉曼光谱的拉曼散射截面、线宽和倍频与基频强度比的影响。虽然共振效应和电子-声子耦合作用在不同温度下对拉曼光谱都有一定影响，但研究发现不同温度下共振效应对拉曼光谱的影响要大于电子-声子耦合，且电子-声子耦合对谐波的影响更小。这是由于随着温度的降低，发生红移的紫外可见吸收光谱，使拉曼光谱中514.5 nm激发光更接近00吸收峰，明显的增强了分子的共振效应，使其拉曼散射截面，线宽，倍频与基频强度比随温度有很大变化。该研究对共振效应和电子-声子耦合的研究为研究温度对胡萝卜素等线性多烯分子性质的影响提供一定实验和理论依据。

The Effect of Resonance Effect and Electron-Phonon Coupling on Resonance Raman Spectra of Linear Polymers

Linear polymers are characterized by their high intensity and information-rich resonance Raman spectroscopy，which has applications in biology, photoelectric materials and medicine. However, β-carotene molecules with conjugated double bonds are the most representative of polyene molecules. It is worth researching the effects of π-electron and CC vibration interaction on absorption spectrum and Raman spectroscopy, and the effects of resonance enhancement effect and electron-phonon coupling on the relative intensities, frequency and line shape Raman spectra. The resonance Raman spectra and UV-visible spectrum of β-carotene in 1,2-dichloroethane solution are obtained from the 283 to 223 K temperature range. We research the effects of the resonance effect and electron-phonon coupling on absorption and Raman spectra. With decreasing temperature, the Huang-Rhys decreases, indicates the CC bond vibration weakened and the molecular system energy decreases, which cause the absorption spectra redshift; in addition, with decreasing temperature, the degree of structural order of molecule increases, indicates the electron-phonon coupling interaction increases, which enhance the effect of electronic energy gap on the CC vibration, so, the Raman frequency shifts to the lower wavenumber, namely, the Raman spectra redshift. Calculations show that as the temperature decreases, the Raman scattering cross-section of the CC bonds increases, the Raman bandwidths of the CC bonds narrow, the ratio of overtone to fundamental mode increases. We compare and analyze the effects of resonance effect and electron-phonon coupling on the Raman cross-section, linewidth and the intensity ratio of overtone to the fundamental mode of Raman spectra. Although both the resonance effect and electron-phonon coupling can influence the Raman spectra at different temperatures, the resonance effect is more significant than the electron-phonon coupling for the Raman spectra, and electron-phonon coupling is more negligible effective on harmonics. With the temperature decreasing, the redshift of the absorption spectrum makes the 514.5nm excitation light in the Raman spectra closer to the 00-absorption peak, which significantly enhances the resonance effect of the molecule and makes the Raman scattering cross-section, linewidth, and the intensity ratio of the frequency of the overtone to fundamental modes significantly change with the temperature. The researches of electron-phonon coupling and resonance effect provide some experimental and theoretical basis for studying the effects of temperature on the properties of linear polyenes such as carotene.