INELASTIC INCOHERENT NEUTRON-SCATTERING STUDY OF MOLECULAR MOTIONS OF NORMAL-NONADECANE IN UREA CLATHRATE

Inelastic incoherent neutron scattering experiments were performed on semi-oriented samples of C19H40-urea chlatrates over the 1.5-306 K temperature range. Using appropriate sample orientations and different instrumental resolutions, all the motions parallel or perpendicular to the main chain axes were analyzed in the 0-400 cm-1 frequency range. In the quasielastic region and for the Q momentum transfer vector parallel to the chain axes, a side peak attributed to a longitudinal acoustic mode was evidenced at 12 cm-1 at 1.5 K (overdamped at higher temperatures) in addition to large quasielastic broadenings due to restricted translational motions. For Q perpendicular to the chains, a diffusive rotational process was also evidenced in the disordered solid phase. All these results are discussed and compared to literature data. © 1990 American Institute of Physics.