The kinetics of sorption and subsequent desorption of normal H2 and Ne gases in C60 powder was investigated at 12 to 292K using the method of direct pressure measurement. The measured characteristic times for filling the octahedral interstitial sites of fullerite with gas molecules were used to obtain the temperature dependences of the diffusion coefficients in fullerite for H2 and Ne. Upon cooling down below room temperature the diffusion coefficients of the impurities were found to initially decrease in both solid state solutions and then rise steeply below 90K (H2) or 100K (Ne). At the lowest temperatures reached in the experiments, the temperature dependence of the diffusion levelled out. The features revealed were attributed to competition between thermally activated diffusion, which was dominant at comparatively high temperatures, and quantum diffusion, which prevailed at low temperatures.

Diffusion of H2 and Ne Impurities in Fullerite C60. Quantum Effects. Dolbin, A.V., Eselson, V.B., Gavrilko, V.G., Manzhelii, V.G., Vinnikov, N.A., Popov, S.N.: Low Temperature Physics, 2012, 38[10], 962-5