Endohedral complexes with noble gases

Endohedral complexes with noble gases as the guests are of interest for several reasons. First of all, as previously mentioned in Section 2, their existence is well documented thanks to the collisional injection experiments [17,18,19,20,41]. Second, encapsulation of noble gas atoms was proposed as a means of increasing the stiffness of the Ceo cage in order to obtain materials harder than the undoped fullerite [42]. From the theoretical standpoint, calculations on endohedral complexes with noble gases provide a practical test of the validity of the theory outlined in Section 4. 

HF/DZP values, ionization potentials from Koopmans theorem. Exponents of the polarization functions ( (He)=1.000, Q(Ne)=1.000, Q(Ar)=0.696. 

Guest Orbital Negative orbital energy -e [eV] -Ae [eV] in vacuo in endohedral complex 

On the other hand, in the Ceo Ar complex, only the Is, 2s, and 2p core orbitals conform to the uniform shift. The valence 3s and 3p orbitals are diffuse enough to mix with the orbitals of the Ceo cage and lose their clear-cut identity. For this reason, the theory of Section 4 is not suited for this complex. The orbital energies and shifts given in Table 6 in parentheses refer to the molecular orbitals that have the largest overlap with the 3s and 3p orbitals of the host. One should note that the mixing is not severe for the HOMO of the Ceo cluster, leaving 

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Figure 3. The occupied orbital energy levels in the Cgo cluster and its endohedral complexes with noble gases. Only the orbitals with energies greater than -35 eV are shown.

Collision-induced fragmentation of Ceo" (n = 1 3) with the noble gases helium and neon at high energy (typically 6keV) results in the formation of encapsulated products, e g. [He C6o]"" The retention of the gas atoms in the fragmentation products [He C2m]" (2w = 58, 56, 54, etc.) is consistent with endohedral complex formulation. Furthermore, [He C6o] has been neutralized in the gas phase to produce He C6o (lifetime >90 p,s), which was then successfully... 

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