EN
Electronic spectra of radical cations of dihydroxynaphthalenes with C_{2v} and C_{2h} symmetry are calculated using an open-shell SCF method with configuration interaction (CI). The characteristic behaviour of electronic transitions depending on the positions of the hydroxyl substituents is discussed. An interesting aspect of this work is the estimation of the first ionization potentials (IP's) of neutral dihydroxynaphthalenes from the energy of the lowest non-Koopmans state for their radical cations. This method for the prediction of IP's is found to be at least as good as that of the Koopmans' theorem with energy correction due to bond perturbation.