On the differences between neutral and negatively charged C-60 dimers

The optimized ground state geometries and total energies have been determined for C-60 dimers with various structures. Neutral as well as negatively charged dimers were considered. Semiempirical calculations were performed, with three different parametrizations: MNDO, AM1, and PM3. For the neutral and the charged dimers different structures have been found at the global energy minima. In the neutral case, the well known 66/66 cycloaddition product with D-2h symmetry was found to be the most stable configuration. In contrast, the charged dimer had a different structure: it is bound through a single carbon atom on each C60 moiety, the two balls being in trans position (C-2h symmetry). This is in accord with X-ray results on the quenched phase of A(1)C(60) (A=K,Rb) Some results of the vibrational analysis on these dimers (neutral as well as charged) are also presented in this paper.