C2H2•••CO complex and its radiation-induced transformations: a building block for cold synthetic astrochemistry

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 center dot center dot center dot 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 center dot center dot center dot 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 C-3 species, whereas the acetylenic C-H bond cleavage yielding ethynyl radical appears to be a minor process. Prolonged irradiation results in dehydrogenation, while the C-3 skeleton is retained. The interpretation of the C2H2 center dot center dot center dot 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.

Automated summary

This study investigates radiation-induced synthetic chemistry in a C2H2-CO system at the molecular level using a matrix isolation approach. It shows that X-ray radiolysis of the C2H2 ・ CO complex leads to the formation of various C-3 species, with ethynyl radical formation as a minor process. The study suggests that the complex may serve as a building block for cold astrochemistry in mixed interstellar ices and discusses the implications of the results for astrochemistry.