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Interstellar Detection of Methyl Isocyanate CH3NCO in Sgr B2(N): A Link from Molecular Clouds to Comets

By SpaceRef Editor
October 1, 2015
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A new interstellar molecule, CH<sub>3</sub>NCO (methyl isocyanate), has been detected using the 12 m telescope of the Arizona Radio Observatory (ARO). CH<sub>3</sub>NCO was identified in spectra covering 48 GHz (68-116 GHz) in the 3 mm segment of a broadband survey of Sgr B2(N). Thirty very favorable rotational lines (Ka = 0 and Ka = 1 only; Eu < 60 K) originating in five consecutive transitions (J = 8 → 7, 9 → 8, 10 → 9, 11 → 10, and 12 → 11) in both the A and E internal rotation species are present in this frequency range. Emission was observed at all of the predicted frequencies, with seventeen lines appearing as distinct, uncontaminated spectral features, clearly showing the classic a-type, asymmetric top pattern, with TR* ~ 20-70 mK. The CH3NCO spectra also appear to exhibit two velocities components near VLSR ~ 62 and 73 km s−1, both with ΔV1/2 ~ 10 km s−1 – typical of molecules such as CH<sub>2</sub>CHCN, HNCO, and HCOOCH<sub>3</sub> in Sgr B2(N). The column density of CH<sub>3</sub>NCO in Sgr B2(N) was determined to be Ntot ~ 2.3 x 1013 cm−2 and 1.5 x 1013 cm−2 for the 62 and 73 km s−1 components, corresponding to fractional abundances, relative to H2, of f ~ 7.6 x 10−12 and 5.0 x 10−12, respectively. CH<sub>3</sub>NCO was recently detected in volatized material from comet 67P/Churyumov-Gerasimenko by Rosetta’s Philae lander, with an abundance ~1.3% of water; in Sgr B2(N), CH<sub>3</sub>NCO is roughly ~0.04% of the H2O abundance.

DeWayne T. Halfen, Vadim V. Ilyushin, Lucy M. Ziurys
(Submitted on 30 Sep 2015)

Comments: 14 pages, 3 tables, 3 figures, 1 machine-readable table in ApJ (Letters) Oct. 2, 2015 issue
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1509.09305 [astro-ph.SR] (or arXiv:1509.09305v1 [astro-ph.SR] for this version)
Submission history
From: DeWayne Halfen
[v1] Wed, 30 Sep 2015 19:25:33 GMT (266kb)


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