Rotational tunneling in CH4 under pressure (CH4 III)

Abstract

High resolution neutron inelastic scattering techniques were used to measure tunneling spectra of methane (CH₄) in its phase III. By increasing the pressure from 0.6 to 1.8 kbar the tunneling lines shift by about a factor of 1.5. The rather complicated spectra can be equally well described by two simple structural models. Both contain two inequivalent molecular sites of low symmetry. They already have provided a rather good fit of the spectrum of CD₄ III. An exponent n = 8±2 of an effective intermolecular potential V∼r⁻ⁿ is obtained by analyzing the pressure dependence of the tunneling frequencies.