COLLECTIVE LOW-FREQUENCY EXCITATIONS IN A MOLECULAR GLASS

The collective dynamics of an organic molecular glass former has been investigated by means of coherent inelastic scattering of neutrons at several temperatures below the glass transition. The excitations obser ved by means of the inelastic neutron scattering response are characte rized by the wavevector dependences of their average frequencies. The inelastic spectra are analysed on the basis of a lattice dynamics calc ulation for the polycrystalline reference state as well as a molecular dynamics simulation of a computer-generated glass. The excitation fre quencies are discussed in terms of average omega(m) quantities, define d as the peak maxima of the longitudinal current-current autocorrelati on function- An assessment of the reliability of the simulation result s is finally made by comparison with the experimentally accessible mag nitudes.