Temporary anion states of fluorine substituted benzenes probed by charge transfer in O2-·C6H6-xFx (x = 0-5) ion-molecule complexes.

The broadband photoelectron source realized by detaching O2-·X (X = neutral unsaturated molecule) complexes offers a unique opportunity to probe temporary anion states of the unsaturated species. Detachment of the ion molecule complex typically accesses a dissociative portion of the neutral potential, creating a continuum electron source that can undergo scattering with X. We present the application of this new approach to electron-neutral scattering toward a study of the series of fluorinated benzenes via photoelectron spectroscopy of O2-·C6H6-xFx (x = 0-6) measured with several photon energies. We compare these spectra to the reference O2-·hexane spectrum and observe evidence of temporary anion states of C6H6-xFx for species with x = 0-5 in the form of enhanced signal intensity at electron kinetic energies coinciding with the energies of the temporary anions. Furthermore, we observe autodetachment features in the x = 3, 5 spectra. Results of calculations on the isolated symmetric isomer of C6H3F3 suggest that the molecule cannot support a weakly-bound non-valence state that could be associated with the observed autodetachment. However, C6HF5- is predicted to support a valence bound state, which, if produced by charge transfer from O2- with sufficient vibrational energy, may undergo autodetachment. Finally, the [O2·C6F6]- spectrum is unique insofar as the spectrum is substantially higher in binding energy and qualitatively different from the x = 0-5 spectra. This result suggests much stronger interactions and charge delocalization between O2- and C6F6.