CN and CCH azirine derivatives, possible precursors of prebiotic molecules: formation and spectroscopic parameters

Abstract

ABSTRACT N-heterocycles are of special relevance in astrobiology but at present no nitrogen-containing heterocycles have been detected in the interstellar medium (ISM). Thus far, the simplest N-heterocyclic compound, 2H-Azirine (c-C2H3N), has not been conclusively identified, despite being searched for. Recently, several cyano and ethynyl derivatives of unsaturated hydrocarbons have been discovered in the cold prestellar core Taurus Molecular Cloud 1 (TMC-1). The purpose of this work is to assess the feasibility of the possible formation of cyano and ethynyl derivatives of azirine (c-C2H2N-CN, c-C2H2N-CCH) under interstellar conditions and provide high-level theoretical spectroscopic parameters of the most relevant cyano- and ethynyl-azirine isomers to facilitate their experimental identification. Six isomers are located for each, cyano- and ethynyl-azirine derivatives, and their interconversion processes are studied. The reactions of 2H-azirine with the CN or CCH radicals in the gas phase are explored as possible formation routes of cyano and ethynyl azirine. We found that the formation processes of the most stable isomers, namely 3-cyano-2H-azirine, 2-cyano-2H-azirine, 3-ethynyl-2H-azirine, and 2-ethynyl-2H-azirine, are exothermic and barrier free. Thus, these compounds stand out as potential targets to be searched for in space. Based on the newly determined rotational spectroscopic parameters, which also account for 14N hyperfine splittings, we compile a line catalogue for each system up to 50 GHz as a preliminary and required step to characterize these molecules experimentally, whether in the laboratory or directly in the ISM.