Photoinduced Rydberg ionization (PIRI) spectroscopy of the (B)over-tilde state of the fluorobenzene cation

Vibrationally resolved PIRI spectra of the (B) over tilde state of the fluo robenzene cation via the origin, 16a, 6b, and 11 vibrational modes in the g round ionic state require are assignment of the accepted state symmetry. On the basis of lower resolution studies, the (B) over tilde <--- (X) over ti lde. transition has been previously assigned as an electronically forbidden B-2(2) <-- B-2(1) transition. Vibrational analyses of the spectra observed via various ground-state nonsymmetric vibrations, particularly from the 16 a vibrational mode, unambiguously locate the origin of the transition at 21 075 cm(-1), resulting in the reassignment of the ionic state as B-2(1). Ab initio calculations, while riot conclusive, also suggest that the (B) over tilde <-- (X) over tilde transition is an allowed pi to pi transition.