A theoretical determination of the low-lying electronic states of the p-benzosemiquinone radical anion

The low-lying electronic states of the p-benzosemiquinone radical anion are studied using multiconfigurational second-order perturbation theory (CASPT 2) and extended atomic natural orbital (ANO) basis sets. Vertical excitatio n energies at the optimized geometries of the anion and the neutral molecul e are computed. In light of the present theoretical results, the informatio n provided by different spectroscopic techniques, such as UV/vis absorption , excitation, fluorescence, electron photodetachment, and electron scatteri ng, is rationalized. CASSCF force fields are employed to compute vibronic i ntensities of the two lowest-energy pi-pi* transitions in order to solve co ntroversial assignments and to give an interpretation of the available reso nance Raman data.