Vibrational Spectra of Mixtures of Isotopomers of Formamide. Anomalies in the Carbonyl Stretching Region
Vibrational Spectra of Mixtures of Isotopomers of Formamide. Anomalies in the Carbonyl Stretching Region
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DOI：
10.1021/j100071a009
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发表时间：
1994-05
期刊：
影响因子：
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通讯作者：
A. Mortensen;O. Nielsen;J. Yarwood;V. Shelley
中科院分区：
文献类型：
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作者：
A. Mortensen;O. Nielsen;J. Yarwood;V. Shelley
本文报道了HCONH_2和HCOND_2液体混合物的红外光谱和拉曼光谱。与预期相反，各向同性的拉曼光谱的混合物显示只有一个羰基伸缩带，其位置取决于混合物的组成。它表明，明显的崩溃的频带是不是由于快速交换不同的“网站”之间（即快速交换限制）。以前在固体中也观察到过类似的现象。因此，该现象可能反映了液体甲酰胺在接近其熔点时的“类固体”行为。拉曼光谱的去偏振分量和羰基伸缩带的IR光谱在近似相同的频率处观察到，而各向同性分量在较低的频率处观察到（非重合）。对于NH2弯曲模式观察到相同的情况。这种模式的非符合分裂示towelow模型的同位素异构体的二元混合物开发的洛根。红外和拉曼谱带的不对称性可以用两个“位点”来解释，一个属于氢键键合的物种，另一个属于不与羰基形成氢键的“自由”物种，但可能与其他甲酰胺分子的羰基形成氢键。
The infrared and Raman spectra of liquid mixtures of HCONH2 and HCOND2 are presented. Contrary to what is expected, the isotropic Raman spectra of the mixtures show only one carbonyl stretching band, whose position depends upon the composition of the mixture. It is shown that the apparent collapsing of bands is not due to fast exchange between different “sites”(ie the fast exchange limit). Similar phenomena have been observed previouslyin solids. Thus, the phenomenon might reflect “solid-like” behavior of liquid formamide close to its melting point. The depolarized component of the Raman spectrum and the IR spectrum of the carbonyl stretching band are observed at approximately the same frequencies, whereas the isotropic components are observed at a lower frequency (noncoincidence). The same is observed for the NH2 bending mode. The noncoincidence splitting of this mode is shown tofollow a model for binary mixtures of isotopomers developed by Logan. The asymmetry of the IR and Raman bands can be explainedin terms of two “sites”, one belonging to a hydrogen-bonded species and the other to a “free” species without hydrogen bonding to the carbonyl group, but maybe forming hydrogen bonds to the carbonyl group of other formamide molecules.