Inversion and torsion of the HNCH3 group in the microwave spectrum of N-methyl-p-fluoroaniline

A reinvestigation of the microwave spectrum of N-methyl-p-fluoroaniline shows this molecule to have low lying excited vibrational states associated with the inversion and torsion of the HNCH3 group similar to N-methylaniline. The experimental data indicate a greater tendency towards a planar configuration at the nitrogen atom and a lower barrier to inversion compared to p-fluoroaniline.