脂肪族聚酰胺振动光谱的密度泛函理论研究

Theoretical study of vibrational spectra of aliphatic polyamide by density functional theory

采用密度泛函理论DFT-B3LYP方法,在6-31G基组水平上对3种脂肪族聚酰胺尼龙2(PA2),尼龙4(PA4)和尼龙6 (PA6)的低聚物OA2,OA4和OA6构型进行优化,得到基态稳定构型;在优化构型基础上计算了分子振动谐性力场,并对理论谐性力场进行了简正坐标分析,得到了低聚物红外光谱及拉曼光谱,用标度因子0.96对计算频率校正。对照实验值,根据振动模式对其特征峰进行了指认。并讨论了由不同长度亚甲基链组成的聚酰胺对振动光谱的影响。

Three kinds of hydrogen-terminated oligomers （OA2, OA4 and OA6） of aliphatic amides （polyamide 2, polyamide 4 and polyamide 6） were optimized on DFT-B3LYP method and 6-31G^＊ basis set. The vibrational force fields of three kinds of oligomers were calculated on DFT-B3LYP method and 6-31G^＊ basis set on the optimized strctures too. These infrared and Raman intensities of three kinds of oligomers were obtained on the basis of these normal vibrations. The theoretical frequency Was scaled by 0.96. The assignment of the vibrational fundamentals was also performed according to experimental results. The effection of different chain length of methylene on vibritional spectra of polyamides was discussed.