Raman spectra of polycrystalline acids CH3COOH, CH3COOD, CD3COOH, CD3COOD at 90 deg K

Raman spectra from 4000 to 40 cm–1 of the acids CH3COOH, CH3COOD, CD3COOH, and CD3COOD in polycrystalline state have been studied. An assignment of the intramolecular vibrations is proposed, and the Raman and infrared data are compared. Seven bands due to external modes, five of which correspond to intermolecular vibrations of the hydrogen bond O — H ... O, have been identified. The structure and width of the νOH and νOD bands are discussed; the interpretation of the sub-bands in terms of combinations of intramolecular vibrations is confirmed. The half-width of the νOH band can be reduced by an order of magnitude with the lowering of temperature and deuteration, which shows that the anharmonicity of the νOH vibrator represents the determining factor for the intrinsic width.