Abstract The rotational spectra of the v 6 = 1 and v 6 = 2 torsional states of CH 3 C 35 Cl 3 have been measured in the millimeterwave range and accurate spectroscopic constants have been determined. The equilibrium structure, the torsional frequency and the barrier to internal rotation have been calculated ab initio. These results are shown to be compatible with the absence of splittings in the rotational spectra.