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Endohedral cage compounds have been considered as possible candidate species for molecular memories. In this report, computations are carried out on four hypothetical He-containing endohedral systems, He@C14H16 (isogarudane and garudane cages) and He@C36 (D6h and D2d cages), and two hypothetical N-containing endohedral systems, N@C36 (D6h and D2d cages). Geometry optimizations are followed by vibrational analysis in some cases. The geometry optimizations can indeed produce local energy minima for the endohedral systems. While in N@C36 D6h the nitrogen atom has a central location, in N@C36 D2d it exhibits a bonding pattern. Thermodynamic and kinetic stability aspects are also discussed.

It has been found that, at low temperatures and small values of the reduced moment of inertia, the conventional formula for the partition function of free internal rotation leads to negative values for the contribution of free internal rotation to the entropy term. It was noted that the reason for this erroneous limiting behavior of the partition function and the thermodynamic functions derived from it lies in the impossibility of approximating the summation through integration under these limiting conditions. An improved formula for the partition function of free internal rotation is suggested, exhibiting correct limiting behavior. The thermodynamics of association of HF and C1F is reevaluated using this new formula, and considerable differences are found compared to the conventional approach.(1) Part 14 in the aeries Multimolecular Clusters and Their Isomerism; for part 13, see ref 21.(2) E.g., N. Davidson, "Statistical Mechanics", McGraw-Hill, New

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