The low-frequency dynamics of different solid phases of ethanol ͑fully ordered crystal, orientational glass, and true structural glass͒ is investigated by measurements of low-temperature specific heat as well as determination of the vibrational densities of states by inelastic neutron scattering. Such polymorphism provides a unique benchmark to study the relative importance of different kinds of disorder on glass-dynamics properties. The measurements are carried out both for hydrogenous and fully-deuterated samples. Large isotopic effects are found for the excess contributions ͑i.e., non-Debye͒ to the specific heat of the disordered solids, which have clear correlates in the low-frequency spectra. ͓S0163-1829͑98͒05626-4͔

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The far infrared ͑FIR͒ spectra of various isotopic species of ethanol ͑-h 6 ,-d 1 , and-d 3 ͒ are analyzed from MP4͑͑SDQT͒ ab initio calculations using models in one and two dimensions. From the calculated frequencies and intensities, previous assignments of ethanol-h 6 and-d 1 bands are reviewed. The position of several combination bands are predicted. Ethanol shows two conformers, trans and gauche, and two interacting torsional modes. The torsional barriers have been calculated to be V 3 ͑trans͒ ϭ1226.7 cm Ϫ1 , V 3 ͑gauche͒ ϭ1296.3 cm Ϫ1 , V OH (␣ϭ62°)ϭ404.1 cm Ϫ1 , and V OH (␣ ϭ180°)ϭ423.3 cm Ϫ1. The flexible models in one and two dimensions yields the same OH torsional frequencies, whereas they differ in the methyl group state calculations. The fundamental bands of the ethanol-h 6 have been evaluated at 205.5 cm Ϫ1 ͑OH torsion͒ and 257.0 cm Ϫ1 ͑CH 3 torsion͒ and their corresponding intensities to be 18.650ϫ10 Ϫ4 and 0.662ϫ10 Ϫ4 .