First Detection of Methyl Isocyanate (CH3NCO) in a Solar-type Protostar

We report the first detection of the prebiotic complex organic molecule CH3NCO in a solar-type protostar, IRAS16293-2422 B. This species is one of the most abundant complex organic molecule detected on the surface of the comet 67P/Churyumov-Gerasimenko, and in the insterstellar medium it has only been found in hot cores around high-mass protostars.

We have used multi-frequency ALMA observations from 90 GHz to 350 GHz covering 11 unblended transitions of CH3NCO and 40 more transitions that appear blended with emission from other molecular species. Our Local Thermodynamic Equilibrium analysis provides an excitation temperature of 232±41 K and a column density of (7.9±1.7)×1015 cm−2, which implies an abundance of (7±2)×10−10 with respect to molecular hydrogen.

The derived column density ratios CH3NCO/HNCO, CH3NCO/NH2CHO, and CH3NCO/CH3CN are ∼0.3, ∼0.8, and ∼0.2, respectively, which are different from those measured in hot cores and in comet 67P/Churyumov-Gerasimenko. Our chemical modelling of CH3NCO reproduces well the abundances and column density ratios CH3NCO/HNCO and CH3NCO/NH2CHO measured in IRAS16293-2422 B, suggesting that the production of CH3NCO could occur mostly via gas-phase chemistry after the evaporation of HNCO from dust grains.

R. Martín-Doménech, V. Rivilla, I. Jiménez-Serra, D. Quenard, L. Testi, J. Martín-Pintado
(Submitted on 16 Jan 2017)

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1701.04376 [astro-ph.SR] (or arXiv:1701.04376v1 [astro-ph.SR] for this version)
Submission history
From: Rafael Martín-Doménech Mr.
[v1] Mon, 16 Jan 2017 18:03:40 GMT (1019kb)
https://arxiv.org/abs/1701.04376

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