2021MNRAS.501.1202D

Complex organic molecules from extraterrestrial source are expected to have contributed to the Early Earth chemistry. Methylamine (CH₃NH₂)has already been observed in the interstellar medium (ISM) and is generally related to the formation of glycine, although the latter has not been identified in the ISM yet. In this work, a chemical model for CH₃NH₂ was investigated, comprising twenty-eight reactions and including reactions involving NH₃ and HOOC, aiming to understand the main routes for formation and decomposition of methylamine and also to infer about the chemical behaviour of glycine in the ISM. Calculations were performed at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level and rate coefficients were calculated adopting the canonical variational transition state theory (CVTST), in the temperature range 100 to 4000 K, including tunnelling effects. Starting from HCN, the preferred pathway for methylamine formation is through consecutive hydrogenation steps, forming CH₂N, CH₂NH, and CH₂NH₂ intermediates. Considering the decomposition, dissociation into CH₃ and NH₂ is the most favourable step. NH₃ and HCN are common compounds in interstellar ice analogues and react producing NH₂ and CH₂N through NH₂NCH₂ and H₂NCH₂N intermediates. The latter is proposed here and spectroscopic data for any future experimental investigation are given. Finally, an extension to the ISM glycine chemistry is explored and routes to its formation, from the simplest compounds found in interstellar ices, are proposed.