Lattice vibrations and molecular rotation in solid methane near the melting point

Abstract

The neutron inelastic incoherent scattering method (IINS) was used for studying the lattice-molecular dynamics in solid methane near the melting point. The neutron spectrum was compared with a theoretical one obtained on the following basis: the molecules rotate in a hindering crystal field and simultaneously perform translatory vibrations which correspond to a Debye temperature of ca. 50 K. The non-occurrence of distinct rotational peaks in the experimental spectrum was interpreted as giving evidence of some rotational hindrance. Agreement between the theory and experiment for the scattered neutron intensity in the low energy transfer region supports the accepted translatory model. A possibility of translation-rotation interaction is discussed.