Noble gas dimers confined inside C70
The potential energy surfaces for the interior rotation of a series of pairs of noble gas atoms encapsulated in the C70 cavity have been explored. He2@C70, Ne2@C70, Ar2@C70, HeNe@C70, HeAr@C70 and NeAr@C70 were chosen as case studies. Our calculations suggest stable minima with the two noble gas atoms lying along the symmetry axis of the fullerene. Transition states for the rotations are expected to occur when the two atoms are located in the symmetry plane perpendicular to the C5 axis. The energy barriers for the rotations are predicted to be in the 5–64 kcal mol−1 range, significantly increasing with the size of the noble gas atoms inside C70. These energy barriers lead to a wide range of rate constants, including those characteristic of very fast internal rotations, of the order of k = 2.40 × 109 s−1 for He2@C70, and those describing very slow rotations, of the order of k = 1.80 × 10−33 s−1 for Ar2@C70. It is mandatory to correct for the basis set superposition error to calculate accurate binding energies.