A reinvestigation of the molecular structures, vibrations and rotation of methyl group in o-methylaniline in S0 and S1 states studied by laser induced fluorescence spectroscopy and ab initio calculations.

The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled o-methylaniline have been obtained for the S1 <-- S0 transition, in which some of the bands have been observed and assigned for the first time. The origin of the electronic transition appears at 34,328.4 cm(-1). It was found that the spectra exhibit an important feature corresponding to the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31 + G* and CIS/6-31 + G* show that the optimised structure of o-methylaniline in the ground state is not planar with the amino group having sp3 hybridation-like character due to the existence of lone paired electrons on the N atom. Upon electronic excitation, the C-N bond exhibits a partial double character, as in the case of other aniline derivatives.