2021MNRAS.506.3499Z

In this work, we have examined the radiation-induced synthetic chemistry occurring in an astrochemically important C₂H₂-CO system at the molecular level using a matrix isolation approach. The 1:1 C₂H₂***CO intermolecular complex of linear structure was obtained in the solid low-temperature (5 K) noble gas matrices by deposition of the C₂H₂/CO/Ng (Ng = Ar, Kr, Xe) gaseous mixtures and characterized by Fourier-transform infrared spectroscopy. It was found that the X-ray radiolysis of the C₂H₂***CO complex resulted in formation of C₃O (tricarbon monoxide), HCCCHO (propynal), c-H₂C₃O (cyclopropenone), H₂CCCO (propadienone), and HC₃O (oxoprorynyl radical). This means that the studied complex may be considered as the simplest building block (or minimal size of intermolecular reactor) for cold astrochemistry occurring in mixed interstellar ices. Remarkably, the discovered transformations of the complex actually represent synthetic routes leading to various C₃ species, whereas the acetylenic C-H bond cleavage yielding ethynyl radical appears to be a minor process. Prolonged irradiation results in dehydrogenation, while the C₃ skeleton is retained. The interpretation of the C₂H₂***CO radiolysis mechanism (possible reactions pathways) is provided based on the analysis of kinetic curves and matrix effect. Astrochemical implications of the results are discussed.