Inelastic neutron scattering of methyl tunnelling in isotopic mixtures of dibromomesitylene

► Tunnelling of methyl groups in isotopic mixtures of dibromomesitylene studied by INS. ► The gap for the CH3 surrounded by two bromine atoms is 390 μeV, for CD3 it is 67 μeV. ► The rotation hindering potentials for CH3 and CD3 are the same. ► The tunnelling gap does not depend of the isotopic dilution. ► The tunnelling gap is insensitive to temperature variations.