Effects of Molecular Reorientation in Solid Methane on the Quasielastic Scattering of Thermal Neutrons

Recent neutron‐scattering measurements on solid methane show that the elastic peak is broadened in the high‐temperature phase $\text{(T\hspace{0.17em}>\hspace{0.17em}20.4°}\mathrm{K})$ and that the broadening depends on the momentum transfer in a complicated manner. In the present paper it is suggested that the broadening is due to frequent stepwise reorientation of the molecules. The widths predicted by this model are in qualitative agreement with the experimental results. The average time between successive rotational jumps is estimated to be about 10⁻¹² sec at $\text{T\hspace{0.17em}=\hspace{0.17em}22.1°}\mathrm{K}$ .