Lattice dynamics of methane hydrate

Yamauchi, Hiroki   ; Igawa, Naoki   ; Ishii, Yoshinobu

Inelastic neutron scattering experiments were carried out on powdered methane hydrate. In order to observe the precise spectra inelastic neutron scattering without the influence of incoherent contribution, the fully deuterated sample was used for the measurements. The relatively clear excitation peaks were observed at about 6.5 meV and 10 meV mainly corresponding to the transverse acoustic modes and exhibited only very little temperature dependence at 10 K and 100 K. On the other hand, the small shoulder found around 4 meV at 10 K showed apparent temperature dependence. The scattering intensity of this shoulder appeared to broaden and decrease at 100 K, which can be attributed to the increasing anharmonic contribution to the translational motion of the methane molecules encaged in the large cages.