Lwin Eaindra, Fischer Taija L, Suhm Martin A
Institute of Physical Chemistry, University of Göttingen, Tammannstrasse 6, 37077 Göttingen, Germany.
J Phys Chem Lett. 2023 Nov 16;14(45):10194-10199. doi: 10.1021/acs.jpclett.3c02517. Epub 2023 Nov 6.
Tertiary amines are strong hydrogen bond acceptors. When a water molecule donates one of the OH groups, its in-phase stretching vibration wavenumber is decreased to such an extent that it comes close to the water bending overtone. This gives rise to anharmonic phenomena such as classical Fermi resonance, resonance with multiple-quantum dark states, or combination transitions with low-frequency intermolecular modes. These effects, which contribute to the spectral breadth of room-temperature hydrogen-bonded amine complexes, are disentangled by Fourier transform infrared spectroscopy in pulsed supersonic slit jet expansions. Monohydrates of the amines quinuclidine, -methylpyrrolidine, -methylpiperidine, and dimethylcyclohexylamine exhibit systematic mode coupling signatures. These suggest relatively fast energy flow out of the excited OH stretching fundamental into intra- and intermolecular degrees of freedom of the hydrogen-bonded water molecule. Trimeric complexes are spectroscopically separated from the amine monohydrates.
叔胺是强氢键受体。当一个水分子提供其中一个OH基团时，其同相伸缩振动波数会降低到接近水弯曲泛音的程度。这会引发非谐现象，如经典的费米共振、与多量子暗态的共振，或与低频分子间模式的组合跃迁。这些效应导致了室温氢键胺配合物的光谱展宽，通过傅里叶变换红外光谱在脉冲超声速狭缝射流膨胀中得以解析。奎宁环、N-甲基吡咯烷、N-甲基哌啶和二甲基环己胺的一水合物表现出系统的模式耦合特征。这些表明激发的OH伸缩基态中的能量相对快速地流入氢键水分子的分子内和分子间自由度。三聚体配合物在光谱上与胺一水合物分离。
