Abundant Z-cyanomethanimine in the interstellar medium: paving the way to the synthesis of adenine
Abstract
We report the first detection in the interstellar medium (ISM) of the Z-isomer of cyanomethanimine (HNCHCN), an HCN dimer proposed as precursor of adenine. We identified six transitions of Z-cyanomethanimine, along with five transitions of E-cyanomethanimine, using IRAM 30m observations towards the Galactic Centre quiescent molecular cloud G + 0.693. The Z-isomer has a column density of (2.0 ± 0.6) × 1014 cm-2 and an abundance of 1.5 × 10-9. The relative abundance ratio between the isomers is [Z/E]∼6. This value cannot be explained by the two chemical formation routes previously proposed (gas phase and grain surface), which predicts abundances ratios between 0.9 and 1.5. The observed [Z/E] ratio is in good agreement with thermodynamic equilibrium at the gas kinetic temperature (130-210 K). Since isomerization is not possible in the ISM, the two species may be formed at high temperature. New chemical models, including surface chemistry on dust grains and gas-phase reactions, should be explored to explain our findings. Whatever the formation mechanism, the high abundance of Z-HNCHCN shows that precursors of adenine are efficiently formed in the ISM.
- Publication:
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Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2019
- DOI:
- 10.1093/mnrasl/sly228
- arXiv:
- arXiv:1811.12862
- Bibcode:
- 2019MNRAS.483L.114R
- Keywords:
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- ISM: abundances;
- ISM: clouds;
- ISM: molecules;
- Galaxy: centre;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted in Monthly Notices of the Royal Astronomical Society Letters