CAJ | 학술논문

本文测量了全反式β胡萝卜素在二甲基亚砜中81—25?C范围的紫外—可见吸收和拉曼光谱.结果表明,随温度降低,紫外—可见吸收光谱、拉曼光谱都发生红移,拉曼光谱线型变窄,散射截面增加这些现象的发生是由于随温度降低,β胡萝卜素分子的热无序降低、分子结构有序性增加、π电子离域扩展,有效共轭长度增加,分子的电子能隙变窄.另外,随着温度的降低,溶剂密度增加,由Lorentz-Lorenz关系得知相伴的折射率增加,从而引起吸收光谱的红移. CC键键长增加,使CC键拉曼光谱红移;振动弛豫时间变长,各CC键之间的键长差减小,线宽变窄;但由于声子,π电子耦合加强使CC键拉曼线型不对称程度增加,低频端“肩”扩展, CC键的弱阻尼相干振动增加,使拉曼散射截面增加.
본문측량료전반식β호라복소재이갑기아풍중81—25?C범위적자외—가견흡수화랍만광보.결과표명,수온도강저,자외—가견흡수광보、랍만광보도발생홍이,랍만광보선형변착,산사절면증가저사현상적발생시유우수온도강저,β호라복소분자적열무서강저、분자결구유서성증가、π전자리역확전,유효공액장도증가,분자적전자능극변착.령외,수착온도적강저,용제밀도증가,유Lorentz-Lorenz관계득지상반적절사솔증가,종이인기흡수광보적홍이. CC건건장증가,사CC건랍만광보홍이;진동이예시간변장,각CC건지간적건장차감소,선관변착;단유우성자,π전자우합가강사CC건랍만선형불대칭정도증가,저빈단“견”확전, CC건적약조니상간진동증가,사랍만산사절면증가.
The effects of temperature on the visible absorption and Raman spectra of all-trans-β-carotene dissolved in dimethyl sulfoxide at temperatures ranging from 81 ?C to 18 ?C were determined. The bands of the visible absorption and Raman spectra of all-trans-β-carotene showed red blue shifts. The bandwidth of the Raman spectra becomes narrow. Raman scattering cross-section increases as the temperature decreases. The red shift of the absorption spectrum is attributed to the thermal conformational change-induced decrease in the effective conjugation length in all-trans-β-carotene chains. The molecular structural order increases and theπ-electron delocalization range is extended as the temperature decreases. The red shift in all-trans-β-carotene can be also attributed to the decrease in the liquid density, and the concomitant decrease in the refractive index is shown by the Lorentz-Lorenz relation. The apparent behavior of the temperature-induced band broadening of CC bonds can be associated with the decrease of difference in C–C and C=C bond lengths, and the shorter vibrational relaxation time. The shoulder observed below 1520 cm?1 shows a red shift. The enhancement of coherent weakly-damped CC stretching vibrations may increase the Raman scattering cross-section.