Low-frequency Raman spectra of crystalline and liquid acetic acid and its mixtures with water.: Is the liquid dominated by hydrogen-bonded cyclic dimers?

Abstract

Low-frequency Raman spectra of crystalline and liquid acetic acid, and acetic acid–water binary solutions with varying mole fractions of acetic acid ( x A), are presented in the form of the relative scattering activities, R( ν ̄ ) spectra. The spectrum of scattered light I( ν ̄ ) from crystalline acetic acid at 285 K shows five distinctive bands. Upon the melting, however, the liquid exhibited conspicuous difference in its appearance, although the R( ν ̄ ) spectrum shows two peaks and a shoulder at similar wavelengths to those of the crystalline bands. The spectral change does not directly support the dominance of the cyclic dimers in the liquid. R( ν ̄ ) spectra of acetic acid–water binary solutions suggest a three-state model composed of acetic acid associates, binary associates and water associates for the local structure of the mixtures.