Abstract

Jet-cooled fluorescence-excitation spectra of aniline, aniline-ND₂, p-methylaniline and p-methylaniline-ND₂ will be presented. Two moderately intense peaks in the p-methylaniline spectrum show an unusual multiplet splitting that is not observed in the ring modes. These two transitions also show a large (100 cm⁻¹) deuterium shift in the ND₂ molecule and are thus assigned as evenquanta transitions involving the amine inversion and torsion. The corresponding peaks in aniline are not split, indicating that the splitting is due to the interaction of the CH₃ torsion with large-amplitude amine motions. Given the large separation between the two groups and the evidence that the amine must be in motion (i.e., have a quantum or more in one of its large-amplitude normal modes), an unusual and dynamic coupling mechanism is suggested. We speculate that the amine motion causes an oscillation in the cloud of the ring that the methyl group responds to by means of the hyperconjugation interaction.

© 1990 Optical Society of America