SPECTROSCOPY OF AR@C60. Barbara A. DiCamillo*, Robert L. Hettich, Georges Guiochon**, and Robert N. Compton**. Oak Ridge National Laboratory, Oak Ridge, Tennessee, *UCLA, Los Angeles, California, **University of Tennessee, Knoxville, Tennessee (*NIST address: Building 225, Room A305, NIST, Gaithersburg, MD 20899, 301-975-3241, email: dicamillo@apollo.eeel.nist.gov)

The translational potential energy diagram of a noble gas atom approaching and passing through a C60 molecule suggests that the endohedral form of Ar@C60 is energetically more stable than the exohedral configuration. To explore this assertion, a fullerene exposed to a high pressure argon atmosphere was isolated and characterized by various spectroscopic techniques. An Ar@C60 sample supplied by the group of Saunders and Cross (Yale University) was enriched by a factor of 200 via high performance liquid chromatography. Energies of the Ar 2p orbitals have been determined for Ar@C60 relative to that of Ar@Graphite via x-ray photoelectron spectroscopy. Fourier transform mass spectroscopy charge transfer experiments bracketed the ionization potential between 7.53 and 7.8 eV. Studies suggest that there are two mechanisms for fragmentation. Laser-induced fragmentation shows loss of both C2 and (C2+ Ar) whereas collision-induced dissociation shows only loss of (C2+ Ar). These results show the preference for endohedral encapsulation of argon.