Abstract
Inelastic incoherent neutron spectra of solid CH3F were measured in the μeV and in the meV range. The methyl groups display the effect of rotational tunneling with a splitting of the librational ground state ℏωt =23.1 μeV. All CH3 groups are equivalent. The tunnel splitting and the transition energy to the first excited librational state E01=10.1 meV are reproduced by a rotational potential V(φ)=11.8 meV⋅cos 3φ. A crystal structure different to those of the other halides has to be postulated to understand this potential.

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