Department of Chemistry, School of Education, Shizuoka University, Ohya, Shizuoka, Japan.
J Phys Chem B. 2012 Jan 12;116(1):353-66. doi: 10.1021/jp209119e. Epub 2011 Dec 12.
A combined experimental and theoretical analysis is carried out on the polarized (isotropic and anisotropic) Raman spectra in the spectral region of the C═O stretching (amide I) band of three isotopic liquid mixtures of N,N-dimethylformamide (normal/d(1), normal/d(6), and normal/(13)C═O). Two distinct types of spectral behavior are found for the isotropic Raman spectra: the separate-band behavior (for normal/(13)C═O), where two separate bands (one for each species) appear at all concentrations but with significant intensity bias, and the merged-band behavior (for normal/d(6)), where only one band appears at a frequency between those of the two species and with a band shape noticeably different from the simple overlap of their profiles. An intermediate case between these two limits is also found (for normal/d(1)). These main spectral features, as well as the noncoincidence effect (NCE) observed for all the mixtures and neat liquids, are well reproduced by the calculations, meaning that (1) the computational procedure (carried out in the time domain) incorporates all the important factors that determine the main spectral features, and (2) the band merger and the intensity bias are both controlled by the same type of term (resonant intermolecular vibrational coupling) of the vibrational Hamiltonian that gives rise to the NCE. Based on this result, the one- and two-dimensional infrared spectra of the normal/d(1) 1:1 mixture are calculated as theoretical predictions. For this purpose, an eigenstate-free method is developed to increase the efficiency of the time-domain spectral calculations and to do the calculations on a largest possible system. The calculated spectral features are compared with those of the polarized Raman spectra and discussed.
对 N,N-二甲基甲酰胺（正常/ d(1)、正常/ d(6)和正常/（13）C═O）三种同位素液体混合物的 C═O 伸缩（酰胺 I）带光谱区域的偏振（各向同性和各向异性）拉曼光谱进行了实验和理论综合分析。发现各向同性拉曼光谱具有两种不同的光谱行为：分离带行为（对于正常/（13）C═O），其中在所有浓度下都会出现两个分离的带（每个物种一个），但强度存在显著偏差，以及合并带行为（对于正常/ d(6)），其中只有一个带出现在两个物种之间的频率处，并且带形状与它们的轮廓的简单重叠明显不同。在这两个极限之间也发现了一个中间情况（对于正常/ d(1)）。这些主要光谱特征以及所有混合物和纯液体观察到的非重合效应（NCE）都被计算很好地重现，这意味着：(1) 计算过程（在时域中进行）包含确定主要光谱特征的所有重要因素；(2) 带合并和强度偏差都由振动哈密顿的相同类型项（共振分子间振动耦合）控制，该项导致 NCE。基于此结果，计算了正常/ d(1) 1:1 混合物的一维和二维红外光谱作为理论预测。为此，开发了一种无本征态方法来提高时域光谱计算的效率，并在尽可能大的系统上进行计算。计算的光谱特征与偏振拉曼光谱进行了比较和讨论。
