MOLECULAR DYNAMICS IN GASEOUS AND SOLID METHANE STUDIED BY INELASTIC NEUTRON SCATTERING METHOD

Measurements of the neutron scattering double differential cross section for gaseous methane at 120 K (scattering angles 30° and 130°) and for solid methane at 80 K (scattering angle 30°) were performed. The results for gaseous methane were compared with calculations based on the assumption of free molecular rotations. A deviation from this theory was found for the 30° scattering angle. The results for solid methane were compared with the theory, in which free molecular rotations were assumed, whereas the translations were replaced by a Debye vibrational spectrum corresponding to the Debye temperature 48 K. In the experimental data no distinct discrete rotational peaks were observed. This lack of rotational peaks indicates some rotational hindrance (but by no means leading to a torsional oscillation). A rather good agreement of both theoretical and experimental scattered intensities at small energy transfers favours the choice of the translational model assumed. © 1969.