The source of similarity of the IR spectra of acetic acid in the liquid and solid-state phases

This paper explains the problem of the fair similarity of the νO–H band contour shapes in the spectra of liquid and crystal samples of hydrogen-bonded acetic acid, in contrast to the corresponding spectral properties of formic acid. It has been proven that regardless of the relative arrangement of hydrogen bonds in each phase, the hydrogen-bonded dimeric systems decide about the profile of the bands. Moreover, the model dimers of different symmetry, i.e., the Ci or C2v one of the “side-to-side” type arrangement of moieties, yield nearly identical spectra. Qualitatively similar spectral properties in the νO–D band frequency range were found for deuterium-bonded formic and acetic acid isotopologues.