THE ELECTRONIC-STRUCTURE OF CA-AT-C60

The electronic structure of Ca@C60 in the gas phase was probed by ultr aviolet photoelectron spectroscopy (UPS) of Ca@C60-. The electron affi nity of Ca@C60 was found to be 3.0 eV. The spectrum suggests that Ca d onates its two 4s electrons to the C60t1u LUMO. Ab initio self-consist ent field Hartree-Fock calculations were performed on Ca@C60 at four d ifferent symmetries, I(h), D3d, D5d, and C5v. We found that the C5v sy mmetry has the lowest energy with the central Ca2+ ion 0.7 angstrom aw ay from the center of C60 and that Ca@C60 has a 3A2 triplet electronic ground state in C5v symmetry.