Role of angular electron pair correlation in stabilizing C 2− 60

A pseudo‐potential that was successfully employed in an earlier study by the Compton group is used to describe the binding of a single electron to a C 60 molecule to form C   − 60 . Then, the interaction of a second electron with the C   − 60anion is treated in two manners. First, as performed in the earlier Compton study, a mean‐field (i.e., Hartree–Fock) approach is used to estimate the C   − 60 ‐to‐C   2− 60energy difference for the singlet state of the dianion and, much as in the earlier study, this dianion is predicted to be unstable by ∼0.4 eV. Second, for this same singlet state, a configuration interaction wave function is employed that allows for the angular correlation of the two excess electrons, allowing them to avoid one another by moving on opposite sides of the C 60 skeleton. The energy of the dianion is lowered by 0.3 eV when angular correlation is included, suggesting that the singlet dianion is unstable with respect to electron loss by only ∼0.1 eV. A Coulomb barrier (>1 eV high) and angular momentum barriers then combine to trap electrons of singlet C   2− 60from detaching, thus producing the very long observed lifetimes. In addition, the energy of the lowest triplet state of C   2− 60is also discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006