The structure of aqueous alcohol solutions at the molecular level for many decades has remained an intriguing topic in numerous theoretical and practical investigations. The aberrant thermodynamic properties of water-alcohol mixtures are believed to be caused by the differences in energy of hydrogen bonding between water-water, alcohol-alcohol, and alcohol-water molecules. We present the Raman scattering spectra of water, ethanol, and water-ethanol solutions with 20 and 70 vol % of ethanol thoroughly measured and analyzed at temperatures varying from -10 to +70 °C. Application of the MCR-ALS method allowed for each spectrum to extract contributions of molecules with different strengths of hydrogen bonding. The energy (enthalpy) of formation/weakening of hydrogen bonds was calculated using the slope of Van't Hoff plot. The energy of hydrogen bonding in 20 vol % of ethanol was found the highest among all the samples. This finding further supports appearance of clathrate-like structures in water-ethanol solutions with concentrations around 20 vol % of ethanol.

As a result of the experimental study of water Raman spectra and water–ethanol solutions, it was established that Fermi resonance and Darling–Dennison resonance make significant contribution to the formation of Raman spectra. Basing on the analysis of the spectra using optimization algorithms, the coupling constants W and the contributions of Fermi resonance to spectra in water and aqueous ethanol solutions at various temperatures were calculated. The contribution of the resonance of Darling–Dennison to the formation of the spectra of solutions was analyzed. It was established that Fermi and Darling–Dennison resonances manifested stronger in a 20% solution of ethanol in water in comparison with pure water. These resonances weakened with increasing temperature. This effect was explained from the point of view of strength of hydrogen bonds. Copyright © 2017 John Wiley & Sons, Ltd.

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