Chemical mechanism for the decomposition of CH3NH2 and implications to interstellar glycine Diego N de Jesus, Jean M B A da Silva, Tatiane N Tejero, Gladson de Souza Machado, Neubi F Xavier, et al. Monthly Notices of the Royal Astronomical Society, 2021 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.
Theoretical investigation of the formic acid decomposition kinetics Gladson de Souza Machado, Eduardo Monteiro Martins, Leonardo Baptista, Glauco Favilla Bauerfeldt International Journal of Chemical Kinetics, 2020 Decomposition of formic acid (HCO2H) proceeds via three unimolecular channels: dehydration, decarboxylation, and dissociation, the latter expected to be of minor contribution to the overall kinetics. In addition, despite the similar values reported for the individual activation energies for the dehydration and decarboxylation reactions, experimental works have shown that the former is dominant in the reaction mechanism. These reactions show pressure‐dependent rate coefficients, and the high‐pressure condition is not yet verified at atmospheric pressure. This work aims to investigate the influence of temperature and pressure on the rate coefficients. Hence, theoretical calculations at the CCSD(T)/CBS level have been performed to accurately describe the unimolecular reaction and Rice‐Ramsperger‐Kassel‐Marcus (RRKM) rate coefficients have been calculated and integrated for the prediction of k(T,P) rate coefficients, adopting both strong and weak collision models, over the intervals 0.5‐10 atm and 298‐2200 K. Our results suggest that the isomerization path is important and explains the preference for the (CO + H2O) channel. Rate coefficients for the (CO2 + H2) and (CO + H2O) formations are given, in s−1, as exp(−34404/T) and exp(−33785/T), respectively. The dissociation limit of 107.29 kcal mol–1, with respect the Z‐HCO2H conformer, leading to OH + HCO, via a barrierless potential curve, with rate coefficients, in s−1, expressed as kHCO+OH(T) = 1.68 × 1017 exp(−56018/T). Temperature and pressure dependence for the HCO + OH → CO2 + H2 and HCO + OH → CO + H2O reactions have also been estimated.
