Study of hydrogen bonding in ethanol-water binary solutions by Raman spectroscopy

Raman spectra of ethanol-water binary solutions have been observed at room temperature and atmospheric pressure. We find that with increasing ethanol concentration, the symmetric and asymmetric OH stretching vibrational mode (3286 and 3434cm^-1) of water are shifted to lower frequency and the weak shoulder peak at 3615cm^-1 (free OH) disappears. These results indicate that ethanol strengthens hydrogen bonds in water. Simultaneously, our experiment shows that Raman shifts of ethanol reverses when the volume ratio of ethanol and the overall solution is 0.2, which demonstrates that ethanol-water structure undergoes a phase transition.