Radiation-driven Destruction of N-heterocycles in H₂O-ice mixtures

Abstract

Simple nitrogen (N-) heterocycles are expected to be an abundant class of molecules within the interstellar medium (ISM). Computational and laboratory studies have demonstrated previously that these molecules likely form during the polymerization of acetylene in the presence of hydrogen cyanide (Ricca et al. 2001, Hamid et al. 2014), a process expected to occur in the stellar outflows of carbon-rich AGB stars. This production pathway is analogous to the formation of benzene, which has been detected in the presence of polyacetylenic chains (Cernicharo et al. 2001). Additionally, laboratory studies have demonstrated that N-heterocycles readily form during the irradiation of icy materials. Specifically, Materese et al. 2015 identified pyridine and isoquinoline in the room-temperature residues formed from photolyzed and warmed ices containing water, ammonia, and benzene or naphthalene. More recently, Wang et al. 2024 identified pyrrole and indole in electron-irradiated acetylene and ammonia ice mixtures.