2024MNRAS.534.1542G

Heterocycles have not been detected in the interstellar medium (ISM) yet. However, the direct involvement of some pentagonal heterocycles within the formation of key biomolecules for the origin of life makes the search for these systems in the ISM relevant for understanding whether some of the bricks of life could be formed in the ISM. We have explored the possible formation of the simple heterocycle furan (c-C$_{4}$H$_{4}$O) under interstellar conditions, through the reaction between two interstellar species, $\mathrm{syn}$-vinyl alcohol ($\mathrm{syn}$-VA) and the CCH radical. We employed state-of-the-art quantum-chemical calculations to elucidate the reaction mechanism between the reaction of CCH radical and $\mathrm{syn}$-VA. Kinetic simulations were carried out aiming to quantitatively assess the viability of this reaction in the ISM. We have found a reaction pathway to furan where all energy barriers are submerged. However, the formation of this heterocycle is not feasible because the intermediates leading to furan can evolve through more favourable routes. In contrast, we have found viable pathways for the formation of the four isomers of 1-butenol-3-yne (HCCCHCHOH) (Z-$\mathrm{syn}$, E-$\mathrm{syn}$, E-$\mathrm{anti}$, and Z-$\mathrm{anti}$), which thus are promising species to be detected in the ISM. Our theoretical work indicates that the four isomers of 1-butenol-3-yne should be present in the ISM because the precursors are known interstellar species, and the kinetic simulations indicate that their formation is very likely. We then encourage the observational search of these molecules in the ISM.