RELAXATION AND PHONONS IN VISCOUS AND GLASSY ORTHOTERPHENYL BY NEUTRON-SCATTERING

We present an extended set of incoherent neutron scattering measurements on the van der Waals liquid o-terphenyl, obtained by time-of-flight and backscattering spectroscopy. In the supercooled liquid regime, data from three instruments are combined and analysed in terms of the selfcorrelation S(Q, t). In the time range 1...100 ps, the crossover from alpha- to beta-relaxation is well described by the masterfunction of mode coupling theory, and fitted parameters are consistent with the previously established critical temperature T(c) [Z. Phys. B83, 175 (1991)]. In the glassy regime, vibrations are harmonic and can be described by a density of states. Deviations at low Q are quantitatively explained by a multiple scattering simulation. Throughout the article, experimental difficulties are discussed in some detail.