ИСТИНА

The C2 hydrocarbons (ethane, ethylene, and acetylene) were detected on Titan and Pluto as well as in cometary ices, and therefore, the investigation of radiation effects on these compounds is of significant interest for astrochemistry. In the present study, we focused on the X-ray radiolysis of the C2 hydrocarbons in solid media. The radiation-chemical experiments were performed at cryogenic temperatures with both pure C2 hydrocarbons and C2Hx/Ng mixtures (x = 2, 4, or 6; Ng = Ar, Kr, or Xe; typical concentration is 1/1000). Gases (or gaseous mixtures) were deposited onto a cold KBr substrate mounted in a closed-cycle helium cryostat and then irradiated with X-rays (effective energy ca. 20 keV). Radiation-induced products were detected using FTIR spectroscopy. Our observations of the radiation-induced products in the solid C2 hydrocarbons are mainly in line with the previous reports on the radiation processing of pure hydrocarbon ices. In the case of ethane (C2H6), the principal radiation-induced products are C2H5 and C2H4, and formation of C2H2, CH4, and C4H10 is observed at higher doses. X-ray radiolysis of solid ethylene (C2H4) leads to the production of C2H2 and C2H5, whereas the irradiation of solid acetylene (C2H2) results mainly in the formation of some conjugated hydrocarbons. Results of the matrix-isolation experiments bring some new information about the radiation chemistry of C2 hydrocarbons at a molecular level concerning primary degradation channels of a single molecule. In the case of matrix-isolated acetylene, the C2H2 = C2H + H is the only primary reaction and further dissociation C2H = C2 + H occurs at higher doses. It was found that primary radiation-induced decomposition of matrix-isolated ethylene included both C2H4 = C2H3 + H and C2H4 = C2H2 + H2 (or 2H) reactions, and prolonged radiolysis leads to the decomposition of the primary radiation-induced products. In the case of ethane, we also observed the involvement of ”deep dehydrogenation” channels, i.e. effective formation of C2H2 and C2H4 (in addition to C2H5). From the quantitative measurements of the radiation-induced decay of different C2 hydrocarbons isolated in noble gas-matrices we may conclude that radiation resistance of these molecules increases in a row C2H6 – C2H4 – C2H2. We believe that the results of the present studies make an original contribution to the laboratory simulations of the hydrocarbons chemistry in the space environment. This work was supported by the Russian Foundation for Basic Research (grant 16-33-00859-mol_a).