Role of low-frequency vibrations on sound propagation in glasses at intermediate temperature

We report measurements of the temperature dependence of the sound attenuati on and the fractional change in sound velocity for the glass (G) and orient ational-glass (OG) phases of polymorphic ethanol. Strikingly similar behavi ors are found for both phases despite the OG's underlying crystal (bcc) lat tice. Such similarity, which is also revealed in dielectric spectroscopy an d inelastic neutron scattering measurements, suggests whole molecule small- angle librations as a common microscopic origin for a wide variety of ''gla ssy'' phenomena.