The benzene dication: Energies of excited states determined by double-charge-transfer spectroscopy using OH + and F + projectile ions

Abstract

Double-charge-transfer spectroscopy has been used to measure double-ionization energies of C 6H 6 to electronically excited states of the dication. Since OH + and F + projectile ions were used, it is likely, because of the Wigner spin-conservation rule, that triplet states of the dication were populated. Previously computed energies of certain groupings of triplet states of C 6H 6 2+ are in good agreement with the measured double ionization energies of 24.6±0.5, 27.3±0.5, 29.8±0.5, 31.1±0.5, 32.7±0.8, 34.5±0.8 and 37.2±1.0 eV. Because of the high density of singlet and triplet states, it is only certain that the spin-conservation rule applies to reactions in the present investigation which populate the states with the two lowest energies. Comparison with the calculated data suggests that 24.6 eV is the energy of the 3A 2g state whilst 27.3 eV corresponds to the group of states 3E 1u, 3B 1g, 3E 1g and 3B 2g which have been calculated to be separated by no more than 0.34 eV.