液态聚乙二醇CH_2剪切振动和扭转振动——拉曼光谱和密度泛函理论计算

CH_2 Scissor and Twist Vibrations of Liquid Polyethylene Glycol——Raman Spectra and Density Functional Theory Calculations

提出了一种新方案,以有效洞察液态中共存构象异构体对聚氧乙烯(PEO)实际振动光谱的贡献。通过定义6种-(CH_2CH_2O)-重复单元构象,构建并优化得到4种全同EO构象组合[(TGT)_(10)、(TTT)_(10)、(TTG)_(10)和(GTG)_(10)]和3种其它EO构象组合的构象异构体结构,并在PCM溶剂模型和B3LYP/6-31G(d)理论水平下,对结构进行了优化和振动频率计算。通过振动模式分析,提出描述PEO400各构象异构体的不同CH_2剪切振动和CH_2扭转振动模式的统一标准,确定了4种CH_2CH_2-O-CH_2CH_2链段构象和相关振动模式,以及它们与振动频率大小的关系,并应用于实际拉曼光谱的指认。

A new method is developed to effectively study the contributions of various coexisting conformations to the actual vibrational spectrum of liquid polyethylene oxide （PEO）. By defining six conformations for the -（CH2CH20）- unit, four isomers from the combinations of all the same EO conformations [（TGT）10, （TTT）10, （TTG）10, and （GTG）10] and three isomers from the combinations of other EO conformations were constructed. Their optimized geometric structures and the corresponding vibrational frequencies were then computed. The unified standards that describe the different types of the CH2 scissor and CH2 twist vibrational modes for PEO400 are proposed through the analysis of the normal modes. The relationships between the four CH2CH2-O- CH2CH2 conformations and the various CH2 scissor and CH2 twist vibrational modes and frequencies are determined, and the results are used to assign the practical vibrational spectra.