Radiation-Induced Transformations of CH Molecules in Solid Noble-Gas Matrices: Is Benzene Intrinsically Resistant in Condensed Media?

The radiation resistance of aromatic compounds is one of the key concepts of basic and applied radiation chemistry in condensed phases. Usually, it is attributed to the intrinsic radiation stability of the benzene ring. In this work, we have demonstrated for the first time that the isolated benzene molecules undergo rather efficient radiation-induced degradation in rigid inert media at cryogenic temperatures (comparable to that of aliphatic hydrocarbons), and their stability is essentially determined by the intermolecular relaxation correlating with matrix polarizability. The principal primary products of benzene radiolysis in matrices are phenyl radicals and fulvene. The matrix environment strongly affects the proportion of these species because of external heavy atom effect on the intersystem crossing, which may trigger further reaction pathways. The obtained results may have important implications for the prediction of radiation stability of complex organic systems and polymers. Furthermore, they may contribute to a better understanding of the radiation-induced evolution of aromatic species in cold interstellar media.