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.

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An optical multichannel system is described, used for time-dependent absorption measurements in the gas phase and the liquid phase and for resonance Raman spectroscopy of short-lived transient species in the liquid phase in pulse radiolysis. It consists of either an image converter streak unit or an image intensifier coupled to a TV camera with computerized data handling. The system enables the recording of time-dependent absorption spectra or resonance Raman spectra of short-lived radicals and excited states with single electron and light pulses.

The radical cation of N,N-dimethylpiperazine (DMP) has been studied using time-resolved optical absorption and resonance Raman spectroscopy. Different quantum-chemical methods were used to calculate the molecular structures and vibrational force fields in the ground state of the radical cation and in the resonant excited state. An excellent agreement between theoretical and experimental vibrational frequencies as well as resonance Raman intensities could be achieved. It is concluded that through-σ-bond interaction between the formal lone pair on one amino nitrogen and the odd electron on the other is strong enough to lead to a symmetric charge-delocalized molecular structure of the DMP radical cation, with a chair-type geometry.

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