Stability of interstellar fullerenes under high-dose γ-irradiation: new data

The detection of fullerenes in carbonaceous chondrites and in the geological strata of the Cretaceous-Tertiary boundary layer, associated with the Yucatan bolide impact, can be considered as an indirect evidence of fullerene formation in circumstellar envelopes of mass-losing carbon-rich stars. The large carbon clusters are very stable compounds with the respect to various physical and chemical factors. Nevertheless only scarce data on their behavior under high-dose γ-irradiation are available. This aspect is of crucial importance for the chemistry of interstellar fullerenes, since the existence of the large spherical carbon clusters must finally depend on competition between the rates of their formation and radiation decomposition. In continuation of our studies of the capability of solid C60 fullerene to withstand prolonged γ-irradiation, in the present work we report on a long duration experiment, lasted for ca. 8 months. We found that the degree of C60 decomposition, both in the presence and absence of liquid water, was less than 15%, demonstrating its extreme stability. A similar fullerene stability can be expected in different space environments, where the large carbon clusters are formed, incorporated into interstellar dust particles and subsequently into comets, and travel through the Universe.