Intermolecular interaction in liquid dimethylformamide and its manifestation in Raman spectra

Abstract

AbstractThe 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 CCl4 and dimethyl sulfoxide. A doublet structure of the band is observed in solutions with CCl4 in the 0.2 mole fraction concentration region. The above‐mentioned 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. Copyright © 2003 John Wiley & Sons, Ltd.