NEUTRON-SCATTERING EVIDENCE FOR THE COUPLING OF SHEAR AND REORIENTATIONAL MOTIONS IN THE VISCOELASTIC LIQUID QUINOLINE

The anomalous behavior of several thermal and dynamical properties of liquid quinoline within the temperature range of 260 less-than-or-equa l-to T less-than-or-equal-to 3 10 K is investigated. The neutron quasi elastic scattering spectra are analyzed using, for the purpose, previo us dynamical information available from NMR relaxation and depolarized light scattering. The temperature dependence of the mass-diffusion an d reorientational coefficients is derived from the experimental data, evidencing that only the rotational motion shows a clear deviation fro m Arrhenius behavior. The presence of shear wave excitations which cou ple to reorientational motions is manifested as a strong inelastic bac kground which shows a marked wave-vector dependence.