Noble gas dimers confined inside C70

Abstract

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.