ИСТИНА

Model matrix-isolation studies on radiolysis of astrochemically-relevant molecules may be helpful for better understanding of the radiation chemistry occurring in cold space media. Acetylene is known to occur in various extraterrestrial environments (particularly, in cometary ices), although it is a rather low-abundant species and should mainly exist as an admixture to principal components, such as H2O and CO. Therefore, the radiation-induced transformations of acetylene and its complexes with main interstellar molecules are of significant interest for astrochemistry. Moreover, the studies of the impact of radiation on weak intermolecular complexes may present general interest for basic radiation chemistry. In present work we have examined the low-temperature radiation-induced transformations of C2H2 molecules as well as C2H2···H2O and C2H2···CO complexes using matrix-isolation approach. Matrix samples were obtained by deposition of appropriate gaseous mixtures (C2H2/Y/Ng 1/0÷3/1000; Y = H2O, CO; Ng = Ar, Kr, Xe) onto a cold KBr substrate mounted in a closed-cycle helium cryostat. Quite efficient formation of the C2H2···Y intermolecular complexes was found in the samples containing Y dopant (H2O or CO). The deposited matrices were irradiated with X-rays (effective energy ca. 20 keV) to different doses (up to 200 kGy) at 6 K. FTIR-spectroscopy was used to monitor the composition of deposited samples and radiation-induced decay of the studied species as well as formation of the radiolysis products. Experiments on radiolysis of matrix-isolated acetylene revealed that it undergoes progressive radiation-induced dehydrogenation through formation of C2H radicals to isolated C2 molecules. Radiation resistance of C2H2 at molecular level is somewhat higher as compared to other C2 hydrocarbons[3]. It was found that complexation with both H2O and CO led to intensification of the radiation-induced decomposition of acetylene molecules, i.e. the decay of C2H2···H2O and C2H2···CO complexes is sufficiently faster than that of isolated C2H2 molecules. Radiolysis of C2H2···H2O led to formation of H2CCHOH, H2CCO, HCCO, CO and CH4, whereas the C3O species was observed as main product of the C2H2···CO radiolysis. The mechanisms of the corresponding radiation-induced transformations will be discussed. This work was supported in part by the Russian Foundation for Basic Research (grant № 19-03-00579-a).