Chemical models of interstellar cyanomethanimine isomers

Abstract

<jats:title>Abstract</jats:title> <jats:p>The E-isomer of cyanomethanimine (HNCHCN) was first identified in Sgr B2(N) by a comparison of the publicly available Green Bank Telescope (GBT) PRIMOS survey with laboratory rotational spectra. Recently, Z-cyanomethanimine was detected in the quiescent molecular cloud G+0.693-0.027 with the IRAM 30m telescope. Cyanomethanimine is a chemical intermediate in the proposed synthetic routes of adenine, and may play an important role in forming biological molecules in the interstellar medium. Here we present a new modelling study of cyanomethanimine, using the Nautilus gas-grain reaction network and code with the addition of over 400 chemical reactions of the three cyanomethanimine isomers and related species. We apply cold isothermal core, hot core and C-type shock models to simulate the complicated and heterogeneous physical environment in and in front of Sgr B2(N), and in G+0.693-0.027. We identify the major formation and destruction routes of cyanomethanimine, and find that the calculated abundances of the cyanomethanimine isomers and the ratio of Z-isomer to E-isomer are both in reasonable agreement with observations for selected environments. In particular, we conclude that these isomers are most likely formed within or near the hot core without the impact of shocks, or in the cold regions with shocks.</jats:p>

Diastereoselective Formation of trans-HC(O)SH Through Hydrogenation of OCS on Interstellar Dust Grains

“…The values of our tunneling corrected rate constants, summed to the tentative branching ratios of reaction provided here can be used to improve astrochemical models. Similarly, the here provided data complements recent efforts (Shingledecker et al 2019b(Shingledecker et al , 2020Zhang et al 2020;García de la Concepción et al 2021) to study stereochemistry in the ISM, fundamental in the context of prebiotic chemistry. The high diastereospecificity of this reaction makes trans-HC(O)SH a good case study for the study of isomerization processes in the ISM.…”

Gas-phase Chemistry in the Interstellar Medium: The Role of Laboratory Astrochemistry

“…As mentioned above, C-substituted imines such as cyanomethanimine, ethanimine and propargylimine exist in two forms: Z and E (Melosso et al, 2018;Baiano et al, 2020;Lupi et al, 2020a). As pointed out in several works (see, e.g., Zhang et al (2020);Shingledecker et al (2020)), known reaction mechanisms are not able to explain the isomer abundance ratio obtained from astronomical observations. In Lupi et al (2020a), assuming similar destruction rates for both E and Z forms of propalgylimine and cyanomethanimine, the branching ratios for the CH 2 NH + CCH and, in particular, CH 2 NH + CN reactions were found to semi-quantitatively predict observations.…”

The Beginning of HCN Polymerization: Iminoacetonitrile Formation and Its Implications in Astrochemical Environments

“…Computational studies of HCN dimerization on ice grains have predicted similar unfavorable kinetics . A reaction network study suggests that the cyanide radical and methylene imine might be important precursors to iminoacetonitrile in molecular clouds …”

“… 32 A reaction network study suggests that the cyanide radical and methylene imine might be important precursors to iminoacetonitrile in molecular clouds. 33 …”

“…32 A reaction network study suggests that the cyanide radical and methylene imine might be important precursors to iminoacetonitrile in molecular clouds. 33 In this work, we focus on explaining the formation of iminoacetonitrile in neat liquid HCN. HCN polymerization reactions in polar solutions are known to be base-catalyzed and to proceed in a wide range of temperatures (195−373 K) 34,35 at concentrations ranging from 0.01 M to pure HCN (26.2 M).…”