Neutron inelastic scattering spectra of methane on graphite at the commensurate–incommensurate phase transition

Neutron scattering spectra associated with rotational tunnelling and low frequency vibrations of CH4 adsorbed on graphite at 4 K and coverages from 0.2 to 1.5 monolayers are reported. Particular consideration is given to the changes which occur across the commensurate–incommensurate phase transition. It is shown that the incommensurate phase has a domain wall structure and is not a floating phase as had previously been proposed from theory.