LOW-FREQUENCY RAMAN-SPECTRA OF CRYSTALLINE AND LIQUID ACETIC-ACID ANDITS MIXTURES WITH WATER - IS THE LIQUID DOMINATED BY HYDROGEN-BONDED CYCLIC DIMERS

Low-frequency Raman spectra of crystalline and liquid acetic acid, and acetic acid-water binary solutions with varying mole fractions of ace tic acid (x(A)), are presented in the form of the relative scattering activities, R(<(nu)over bar>) spectra. The spectrum of scattered light I(<(nu)over bar>) from crystalline acetic acid at 285 K shows five di stinctive bands. Upon the melting, however, the liquid exhibited consp icuous difference in its appearance, although the R(<(nu)over bar>)spe ctrum shows two peaks and a shoulder at similar wavelengths to those o f the crystalline bands. The spectral change does not directly support the dominance of the cyclic dimers in the liquid. R(<(nu)over bar>;) spectra of acetic acid-water binary solutions suggest a three-state mo del composed of acetic acid associates, binary associates and water as sociates for the local structure of the mixtures. (C) 1998 Elsevier Sc ience B.V. All rights reserved.