Gas-phase formation of glycolonitrile in the interstellar medium

Abstract

Our automated reaction discovery program, AutoMeKin, has been utilized to investigate the formation of glycolonitrile (HOCH₂CN) in the gas phase under the low temperatures of the interstellar medium (ISM). The feasibility of a proposed pathway depends on the absence of barriers above the energy of reactants and the availability of the suggested precursors in the ISM. Based on these criteria, several radical–radical reactions and a radical–molecule reaction have been identified as viable formation routes in the ISM. Among the radical–radical reactions, OH + CH₂CN appears to be the most relevant, considering the energy of the radicals and its ability to produce glycolonitrile in a single step. However, our analysis reveals that this reaction produces hydrogen isocyanide (HNC) and formaldehyde (CH₂O), with rate coefficients ranging from (7.3–11.5) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ across the temperature range of 10–150 K. Furthermore, the identification of this remarkably efficient pathway for HNC elimination from glycolonitrile significantly broadens the possibilities for any radical–radical mechanism proposed in our research to be considered as a feasible pathway for the formation of HNC in the ISM. This finding is particularly interesing given the persistently unexplained overabundance of hydrogen isocyanide in the ISM. Among the radical–molecule reactions investigated, the most promising one is OH + CH₂CHNH, which forms glycolonitrile and atomic hydrogen with rate coefficients in the range (0.3–6.6) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ within the 10–150 K temperature range. Our calculations indicate that the formation of both hydrogen isocyanide and glycolonitrile is efficient under the harsh conditions of the ISM.