Methyl group tilt and structure from rotational spectra of the CH2DNHCl monodeuterated species

The structure and tilt of the methyl group of CH₃NHCl have been determined by analysis of the three different ground state rotational spectra of the methyl monodeuterated species. The tilt was found to be ?3.5° which is of the same order of magnitude and towards the unshared pair of electrons at the nitrogen atom as in methylamine and its derivatives.The barrier to internal rotation was determined form the A-E splittings of the previously measured transitions and found to be 3781 ± 14 cal/mole for CH₃NHCl and 3784 ± 15 cal/mole for CH₃NDCl, while the values obtained under the assumptions of no tilt and of asymmetric methyl group as in methylamine were 3707 ± 30 cal/mole for CH₃NHCl and 3726 ± 25 cal/mole for CH₃NDCl. Some information has also been deduced on the orientation of the z axis of the principal quadrupole coupling tensor.