A new method for the high-resolution electronic spectroscopy of cations with mass resolution. Optical transitions from Rydberg states converging on the ground state of the cation to states with electronically excited cores are detected by their rapid autoionization. The spectrum of these transitions provide ionic information because the photoabsorption cross-section of a molecule in a high-n Rydberg state closely mirrors the spectrum of the ion core. The technique presented here, called photoinduced Rydberg ionization (PIRI) spectroscopy, is applied in this case to record the (B) over tilde (2)E(2g) --> (X) over tilde (2)E(1g) transition of the benzene cation via the vibrational origin of the (X) over tilde (2)E(1g) ionic state.