Electron scattering on p-benzoquinone anions

Electron scattering on p-benzoquinone anions was studied in a storage ring and the detachment cross-section measured as a function of electron energy. From a fit to a classical model developed for spherical symmetric anions, the threshold was found at 8.4 eV. According to the electron-binding energy, a much lower value, 4.4 eV, is predicted. The deviation is attributed to neglect in the model of the large polarizability of the π-conjugated anion. Ab initio calculations predict a resonance state below 3 eV but its identification is not within reach of the technique due to the thick repulsive Coulomb barrier.