2-巯基-5-硝基苯并咪唑振动光谱的密度泛函理论研究

Theoretical Study on Vibrational Spectroscopy of 2-Mercapto-5-Nitrobenzimidazole by Density Functional Theory

选用密度泛函理论中的B3LYP杂化泛函,在B3LYP/6-31++g(d,p)(C,H,N,S)水平下,优化了2-巯基-5-硝基苯并咪唑分子(MNBMZ)的结构,优化结果表明,2-巯基-5-硝基苯并咪唑分子是一个近平面结构。通过频率计算,获得了2-巯基-5-硝基苯并咪唑分子(MNBMZ)的拉曼光谱,并和实验获得的拉曼光谱图进行了对比,200~800cm^-1波数段实验获得的拉曼谱带波数和理论计算波数相比,有一定程度的蓝移,800~1800cm^-1波数段实验获得的拉曼谱带波数和理论计算波数相比,发生了一定的红移。对实验和理论计算光谱主要振动峰进行线性回归拟合,相关系数r=0.998,标准偏差14.98。实验和理论计算获得的拉曼光谱图基本上是一致的,表明本文选取的DFT理论计算方法是可靠的。结合VEDA4软件对2-巯基-5-硝基苯并咪唑分子的拉曼谱带简正振动模式进行了指认。此外,分析并讨论了2-巯基-5-硝基苯并咪唑分子(MNBMZ)前线轨道及HOMO,LUMO轨道的组成,HOMO和LUMO轨道能级差为3.31eV,电子有从HOMO跃迁到LUMO的趋势。HOMO轨道中S原子的贡献是52.53%,LUMO轨道中硝基N和O原子的贡献分别为23.03%,19.97%和19.36%。采用含时密度泛函理论(time dependent density functional theory,TDDFT)对2-巯基-5-硝基苯并咪唑分子(MNBMZ)的激发态进行了计算分析,计算结果表明甲醇溶剂中2-巯基-5-硝基苯并咪唑分子(MNBMZ)理论计算的吸收波长为213,281和437nm;实验获得的吸收波长223,272和353nm。对研究2-巯基-5-硝基苯并咪唑分子的性质,提供了理论基础。

Raman spectroscopy and optimized geometry of the 2-Mercapto-5-nitrobenzimidazole(MNBMZ)molecule had been calculated at density functional B3LYP level using 6-31++g(d,p)basis set in this paper.Raman spectrum was obtained from the calculation results of the frequencies,and compared with the experimental Raman spectrum.The compared results showed that there is a blue shift in the range of 200~800 cm^-1,however in the range of 800~8 800 cm^-1,there is a red shift.A line of best fit of the experimental Raman frequences versus the calculated ones in the range of 200~1 800 cm^-1,the correlation coefficient and the standard deviation were 0.998 and 14.98.The vibrational mode was assigned on the basis of potential energy distribution(PED)through the VEDA4.In addition,the Frontier HOMO-LUMO orbital and the compositions were discussed based on the calculated results,and the HOMO-LUMO gap was estimated to be 3.31 eV,which indicated that the electron will transfer from the HOMO to LUMO.The contribution of S to the HOMO orbital was 52.53%,and the contribution of N and O in nitryl was 23.03,19.97,19.36 to the HOMO orbital.The excited states were calculated by TDDFT,and the results showed that the adsorption wavelength is 213,281 and 437 nm,but it is 213,272 and 353 nm especially from the experimental spectrum in the methyl alcohol.This study provided a theoretical support for the analysis of MNBMZ.