The wavenumbers of peaks of parallel and perpendicular polarized components of the C O vibration band for dimethylformamide in the Raman spectra differ by 14.5 cm −1 . The difference in wavenumber values decreases and falls to zero on strong dilution with CCl 4 and dimethyl sulfoxide. A doublet structure of the band is observed in solutions with CCl 4 in the 0.2 mole fraction concentration region. The abovementioned non-coincidence of C O vibration band wavenumbers in pure liquid is explained by the complexity of the band, i.e. the presence within the band of two close and overlapped lines with different magnitudes of depolarization ratio belonging to monomeric molecules (high wavenumber) and aggregate formation. In a mixture at strong dilution there remains only one type of formation, and the band acquires a simple shape of a separate line, and the above-mentioned wavenumber difference falls to zero. The experimental results are supplemented by ab initio calculations of normal vibrational wavenumbers and of some parameters for monomeric and dimeric dimethylformamide molecules.

No abstract

The width and shape of the 818 cm-1 band of propan-2-ol in the Raman spectra in aqueous and other solutions were studied. In neutral solvent (1,2-dichloroethane) the band at low contents of the alcohol (0.3 mole fraction) obviously has a dual character. The bandwidth in aqueous solutions passes through a maximum with change in concentration, and the maximum of broadening occurs in the same range of concentrations as described in the literature for the maximum of the intensity of isotropic Rayleigh scattering of light. Dilution of propan-2-ol in acetonitrile leads to the disappearance of only the low-wavenumber asymmetry of band, accompanied by its narrowing. The maximum of line broadening in aqueous solutions is explained by reconstruction of the solution structure. As a result of this reconstruction, the hydrogen atoms of the OH group of the alcohol molecules are free from H-bonding.

The paper presents the calculated spectra of hydrocarbon components of a natural gas (NG), and they are compared with the experimental results. The results of experimental studies of NG show that the region of stretching vibrations of hydrocarbon С-Н bonds, despite the very high level of the Raman signal, is of little use for the quantitative and qualitative analysis. This is due to the fact that the structure of the bands in this region of the spectrum is very complex, and the methane bands with its suppressing content in NG dominate here. The spectra of weak bands of heavy hydrocarbons against the background of very intense bands of methane are almost not revealed. In full, it is difficult to take all the details into account, as can be seen from the previous one. Therefore, we paid a special attention to the determination of the molecular components of NG such as methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10), by calculating the C–H vibrations and determining the spectral region, where they are located. The results of calculations confirm that the frequencies of C–H vibrations of heavy hydrocarbons (ethane, propane, and butane) do lie in the spectral range of 2500–3500 cm−1 of combinational frequencies.