On the stability of endohedral rare gas fullerenes

The stability of He@C-60 and Ne@C-60 is discussed in the context of a spherical model where the carbon atoms are smeared out into a uniform shell. The electronic properties of the 60 pi-electrons together with those of the central atom are treated in the Thomas-Fermi approximation. Simple electrostatic reasoning elucidates the nature of the radial stability of the complex. A method to include nonspherical corrections is outlined. Possible bonding topologies of the central atom and the C-60 cage are discussed, as well as the relevance of these topologies to incipient central atom distortions.