State Key Laboratory of Fine Chemicals, Dalian University of Technology, 2 Linggong Road, Dalian 116024, China.
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
J Chem Phys. 2019 Feb 14;150(6):064317. doi: 10.1063/1.5086095.
Infrared-vacuum ultraviolet (IR-VUV) spectra of neutral dimethylamine clusters, (DMA) (n = 2-5), were measured in the spectral range of 2600-3700 cm. The experimental IR-VUV spectra show NH stretch modes gradually redshift to 3200-3250 cm with the increase in the cluster size and complex Fermi Resonance (FR) pattern of the CH group in the 2800-3000 cm region. Ab initio anharmonic vibrational calculations were performed on low-energy conformers of (DMA) and (DMA) to examine vibrational coupling among CH/NH and to understand the Fermi resonance pattern in the observed spectra features. We found that the redshift of NH stretching mode with the size of DMA cluster is moderate, and the overtone of NH bending modes is expected to overlap in frequency with the CH stretching fundamental modes. The FR in CH groups is originated from the strong coupling between CH stretching fundamental and bending overtone within a CH group. Well-resolved experimental spectra also enable us to compare the performance of ab initio anharmonic algorithms at different levels.
中性二甲胺团簇（DMA）（n = 2-5）的中红外-真空紫外（IR-VUV）光谱在 2600-3700cm 的光谱范围内进行了测量。实验的 IR-VUV 光谱显示 NH 伸缩模式随着团簇尺寸的增加逐渐红移到 3200-3250cm，并且在 2800-3000cm 区域中 CH 基团具有复杂的费米共振（FR）模式。我们对（DMA）和（DMA）的低能构象进行了从头算非谐振动计算，以研究 CH/NH 之间的振动耦合，并理解观察到的光谱特征中的费米共振模式。我们发现，随着 DMA 团簇尺寸的增加，NH 伸缩模式的红移是适度的，并且 NH 弯曲模式的倍频有望与 CH 伸缩基频在频率上重叠。CH 基团中的 FR 源自 CH 基团内 CH 伸缩基频和弯曲倍频之间的强耦合。良好分辨的实验光谱还使我们能够比较不同水平的从头算非谐算法的性能。
