Ground and low lying excited states of phenoxy, 1-naphthoxy, and 2-naphthoxy radicals via anion photoelectron spectroscopy

We present the slow electron velocity map imaging spectroscopy of cryogenically cooled phenoxide, 1-naphthoxide, and 2-naphthoxide anions. The results allow us to examine the ground state and the lowest energy excited state in the corresponding neutral radicals. Care was taken to minimize autodetachment signals in the photoelectron spectra, allowing for more straightforward comparisons with Franck-Condon analyses. The ground states of these three aromatic oxide radicals all have the unpaired electron residing in a pi orbital delocalized throughout the molecule. The electron affinity of 1-naphthoxy is measured to be 2.290(2) eV, while that of 2-naphthoxy is measured to be 2.404(2) eV, both of which are higher than that of the smaller phenoxy molecule at 2.253(1) eV. The first excited states have the unpaired electron residing in a more localized a orbital, yielding measured term energies for the (A) over tilde state of 1.237(2) eV in 1-naphthoxy and 1.068(1) eV in 2-naphthoxy, while that of phenoxy is lower at 0.952(1) eV. The calculated Franck-Condon spectra generally showed good agreement with the experimental spectra, yielding assignments of the more active vibrations in each electronic state. Significant autodetachment signals arising from dipole bound states near the ground states of all three radicals were observed in our efforts to avoid them, and comparably less autodetachment signals were observed near the excited states. Besides this type of non-Franck-Condon intensities in the photoelectron spectra, we also observed minor features arising due to vibronic coupling in the ground states of all three radicals. Published by AIP Publishing.