Slow photoelectron velocity-map imaging spectroscopy of the C9H7 (indenyl) and C13H9 (fluorenyl) anions.

High-resolution photoelectron spectra are reported of the cryogenically cooled indenyl and fluorenyl anions, C9H7(-) and C13H9(-), obtained with slow electron velocity-map imaging. The spectra show well-resolved transitions to the neutral ground states, giving electron affinities of 1.8019(6) eV for indenyl and 1.8751(3) eV for fluorenyl. Numerous vibrations are observed and assigned for the first time in the radical ground states, including several transitions that are allowed only through vibronic coupling. The fluorenyl spectra can be interpreted with a Franck-Condon simulation, but explaining the indenyl spectra requires careful consideration of vibronic coupling and photodetachment threshold effects. Comparison of high- and low-resolution spectra along with measurements of photoelectron angular distributions provide further insights into the interplay between vibronic coupling and the photodetachment dynamics. Transitions to the neutral first excited states are also seen, with term energies of 0.95(5) eV and 1.257(4) eV for indenyl and fluorenyl, respectively. Those peaks are much wider than the experimental resolution, suggesting that nearby conical intersections must be considered to fully understand the vibronic structure of the neutral radicals.