Ring mediated coupling of the internal motions of the amine and methyl groups in <i>p</i>-methylaniline

Abstract

The jet-cooled fluorescence excitation spectra of p-toluidine (p-methylaniline), aniline, aniline (ND2), p-toluidine (ND2), and p-fluoroaniline are presented. The spectra strongly suggest that the internal motions of the methyl and amine groups are coupled, the spectral evidence being a splitting of the amine inversion peak. A group theoretical treatment of the problem is presented using molecular symmetry group methods, however, this treatment appears to fail to properly predict selection rules for the methyl torsion. Possible reasons for this failure are discussed. The symmetry of the potential surface along the nonrigid coordinates is also discussed and a model which explains some of the unusual features of the spectra is presented.