Internal torsional modes in methyl halogenocarbons studied by inelastic neutron scattering

We have studied the internal torsional modes of the methyl groups in a series of substituted methanes of formula (CH3)nCX4–n where n= 1 to 3 and X = F, Cl, Br. (CH3)4C, (CH3)3CI and (CH3)3COD were also studied. The torsional modes have been located in the inelastic neutron scattering (I.N.S.) spectra in down scattering using an inverted beryllium filter spectrometer. The data have been compared with assignments made using other spectroscopic techniques; barriers to rotation and methyl group interaction potentials have been calculated and compared with values in the literature.