2,3-二氯吡嗪的红外、拉曼光谱和密度泛函研究

Infrared,Raman and Density Functional Study of Vibration Spectra of 2,3-Dichloropyrazine

应用KBr压片法、熔融法分别测定了2,3-二氯吡嗪(2,3-DCP)结晶相和液相下400~4 000cm-1范围内的傅里叶变换红外光谱(FTIR),及其600~4 000cm-1内的傅里叶变换拉曼光谱(FT-Raman)。采用密度泛函(DFT)理论之B3LYP方法在6-311++G(2df,2pd)基组水平上优化了该分子的平衡几何结构,基于此结构应用谐性力场计算获得了2,3-DCP的振动频率、红外强度和拉曼活性并进一步计算了直到四阶的非谐性力场,将该力场带入标准旋振哈密顿量并利用二阶微扰理论获得了更加准确的振动频率,相应的红外、拉曼光谱。通过非谐力场获得的振动频率位置结合谐性强度与实验结果比对,对2,3-DCP的各振动带进行了详细指认,采用简正坐标分析方法得到各振动频率的势能分布(PED),首次对2,3-DCP的振动光谱进行了全面归属。结果同时显示:考虑非谐性效应后的理论结果大大提高了振动频率的预测性,用其获得的振动频率能很好的再现实验基频,其与实验值差异大多保持在10cm-1以下,即使在谐振预期很差的高频区域,考虑非谐效应后这种差异也迅速降低到19cm-1以下,这对正确归属和预期振动光谱是十分有帮助的。目前的结论也可推广应用到其他分子体系。

Fourier transform infrared(FTIR)spectra of 2,3-dichloropyrazine in the region 400~4000cm-1 were measured under solid state condition using KBr pellets method and liquid state by the melting method,besides,a Fourier transform Raman(FTRaman)spectra in region 600~4 000cm-1 was recorded.Then equilibrium geometry of 2,3-DCP was optimized,and based on this,the harmonic vibrational frequencies,infrared intensities and Raman activities were calculated using B3 LYP method of the density function theory(DFT)in conjunction with 6-311++G(2df,2pd)basis set,furthermore,a comprehensive anharmonic calculation was also been performed for obtaining more accurate vibrational frequencies using second-order perturbation theory treatment based on quadratic,cubic and quartic force constants.Infrared and Raman spectra were simulated corresponding to theory.Experimental FTIR and FT-Raman bands were compared with those positions of peaks obtained from anharmonic calculations and intensities or activities from harmonic carefully.Each vibrational band was assigned and interpreted in detail with help of potential energy distribution(PED)for the first time.In addition,it was shown that anharmonic results exactly reproduced to experimental data,improved the validity of prediction greatly in vibration frequencies,discrepancies between anharmonic and experimental results were limited to below 10cm-1 in most of vibrational bands,even if in the high energy regions,which have a poor performance for hanmonic calculation,and these differences would be decreased to lower than 19cm-1.It is extremely helpful for assigning and predicting vibrational spectra.Present conclusion can be expanded to others molecular systems.