Vibrational spectra of N,N-dimethylaniline and its radical cation. An interpretation based on quantum chemical calculations

The resonance Raman spectrum of the radical cation of N,N-dimethylaniline (DMA) has been remeasured, and different types of ab initio calculations have been performed to interpret the vibrational spectra of this species and the deuteriated isotopomers previously studied by Poizat et al. (J. Chem. Phys. 1989, 90, 4697). Density functional methods (UBLYP/6-31G*) give results superior to those of Hartree-Fock calculations for the vibrational frequencies of the radical cation of DMA. The same level of theory was also successfully applied to the vibrational spectrum of aniline. CASSCF calculations were used to study the potential energy surfaces of the lowest excited states of the radical cation of DMA, allowing the estimation of resonance Raman intensities. For the neutral DMA conventional HF/6-31G* calculations allow a straightforward interpretation of the infrared and Raman spectra. The calculations lead to revision of some of the previous empirical assignments.