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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Infrared spectra of dimethylquinolines in the gas phase: Experiment and theory
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Infrared spectra of dimethylquinolines in the gas phase: Experiment and theory

机译：气相中二甲基喹啉的红外光谱：实验与理论

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摘要

Infrared spectra of atmospherically important dimethylquinolines (DMQs), namely 2,4-DMQ, 2,6-DMQ, 2,7-DMQ, and 2,8-DMQ in the gas phase at 80 °C were recorded using a long variable path-length cell. DFT calculations were carried out to assign the bands in the experimentally observed spectra at the B3LYP/6-31G* level of theory. The spectral assignments particularly for the C-H stretching modes could not be made unambiguously using calculated anharmonic or scaled harmonic frequencies. To resolve this problem, a scaled force field method of assignment was used. Assignment of fundamental modes was confirmed by potential energy distributions (PEDs) of the normal modes derived by the scaled force fields using a modified version of the UMAT program in the QCPE package. We demonstrate that for large molecules such as the DMQs, the scaling of the force field is more effective in arriving at the correct assignment of the fundamentals for a quantitative vibrational analysis. An error analysis of the mean deviation of the calculated harmonic, anharmonic, and force field fitted frequencies from the observed frequency provides strong evidence for the correctness of the assignment.
机译：使用长可变路径记录了气相中大气中重要的二甲基喹啉（DMQ）的红外光谱，即80°C时的2,4-DMQ，2,6-DMQ，2,7-DMQ和2,8-DMQ长单元。进行DFT计算，以B3LYP / 6-31G *理论水平在实验观察到的光谱中指定波段。使用计算出的非谐波或按比例缩放的谐波频率，不能明确做出特别是C-H拉伸模式的频谱分配。为了解决此问题，使用了按比例分配力场的方法。基本模式的分配通过使用QCPE软件包中UMAT程序的修改版本，通过按比例缩放的力场得出的正常模式的势能分布（PED）来确认。我们证明，对于大分子（例如DMQ），力场的缩放比例更有效地实现了定量振动分析的基本原理的正确分配。对所计算的谐波，非谐波和力场拟合频率与观测频率的平均偏差进行误差分析，为分配的正确性提供了有力的证据。

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