Rotational spectrum and ab initio calculations of N-methylformamide

The microwave spectrum of N-methylformamide has been investigated in the 18-40 GHz frequency range. The rotational spectrum of the conformer with the methyl group cis to the aldehydic oxygen has been assigned. Several rotational transitions of the A sublevel of the ground torsional state have been measured for both normal and N-D isotopic species. The V-3 barrier to the methyl group internal rotation has been obtained from the effective pseudo-defect of inertia. The dipole moment and the N-14 quadrupole coupling constants have been determined. The results of ab initio calculations performed at the HF and MP2 levels are in agreement with the experimental data