Direct experimental probe of the on-site Coulomb repulsion in the doubly charged fullerene anion C702-

Vibrationally resolved photoelectron spectra were obtained for cold C-70(-) and C-70(2-). Accurate values for the first and second electron affinities (EA's) of C-70 were measured as 2.765 +/- 0.010 and 0.02(-0.03)(+0.01) eV, respectively, establishing that C-70(2-) is an electronically stable dianion in the gas phase. The difference between the first and second EA (2.75 eV) provides a direct experimental measure for the on-site Coulomb and exchange interactions between the two excess electrons in C-70(2-). Strong electron correlation effects were also observed between the two excess electrons in C-70(2-).