A QUANTUM-CHEMICAL INVESTIGATION OF FLUORINE IN C-60

Quantum chemical calculations based on the PM3 molecular Hamiltonian a re reported investigating the optimum geometry for the implantation of a fluorine atom in a C-60 molecule. Of he various sites investigated we find the fluorine attached to the outside of the spherical shell en ergetically most favourable. It is shown that in this configuration th e F-atom partially destroys the delocalized electronic state of tile f ullerene in its immediate vicinity creating a locally diamond-like geo metry with C-C bonds of 1.53 Angstrom. Three other possible equilibriu m sites are also found; F occupying a substitutional site, F in the ce ntre of the C-60 molecule, and F at the centre of a C-C bond. Those im plantation sites, however, all have substantially higher total energie s. Investigating higher addition products of the form C60Fi, 1 less th an or equal to i less than or equal to 60, we find an energy minimum a t i approximate to 24. The total energy curve E-tot as a function of i is qualitatively and to a large extent even quantitatively correctly re,reduced by a simple model calculation containing only the C-F bindi ng energy and the nearest neighbour interactions. (C) 1997 Elsevier Sc ience Ltd.