Direct experimental probe of the on-site Coulomb repulsion in the doubly charged fullerene anion C70 2-.

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 0.002 (+0.01/-0.03)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.