Photoelectron spectroscopy of singly and doubly charged higher fullerenes at low temperatures:: C76-, C78-, C84- and C762-, C782-, C842-

Photoelectron spectroscopy of vibrationally cold singly and doubly charged higher fullerenes, C-n(-) and C-n(2-) n = 76, 78, and 84), has been investigated at several photon energies. Vibrationally resolved spectra are obtained for both the singly and doubly charged species, and for n = 78 and 84, transitions from different isomers are also observed. The electron affinities (EAs) Of C-76, C-78, and C-84 are accurately determined to be 2.975 +/- 0.010 eV for C76, 3.20 +/- 0.01 eV for C78(C-2 upsilon), 3.165 +/- 0.010 eV for C-78(D-3), 3.23 +/- 0.02 for C-78(C-2 upsilon(')), 3.185 +/- 0.010 eV for C-84(D-2), and 3.26 +/- 0.02 eV for C84(D-2d). The second EA of the higher fullerenes, which represent the electronic stability of the doubly charged anions, are measured to be 0.325 +/- 0.010 eV for C-76, 0.44 +/- 0.02 eV for C-78(C-2v) 0.53 +/- 0.02 eV for C-78(DA 0.60 +/- 0.04 eV for C78(C-2v(')), 0.615 +/- 0.010 eV for C-84(D-2d), and 0.82 +/- 0.01 eV for C-84(D-2). The spectra of the dianions are observed to be similar to those of the singly charged anions, suggesting that the charging induces relatively small structural changes to the fullerene cages. The onsite Coulomb repulsions in the doubly charged fullerenes are directly measured from the differences of the first and second EAs and reveal strong correlation effects between the two extra electrons. The repulsive Coulomb barriers in the doubly charged fullerenes are estimated from the cutoff in the photoelectron spectra and are found to be consistent with estimates from an electrostatic model.