Issue |
A&A
Volume 654, October 2021
|
|
---|---|---|
Article Number | L1 | |
Number of page(s) | 9 | |
Section | Letters to the Editor | |
DOI | https://doi.org/10.1051/0004-6361/202141989 | |
Published online | 04 October 2021 |
Letter to the Editor
First detection of C2H5NCO in the ISM and search of other isocyanates towards the G+0.693-0.027 molecular cloud
1
Centro de Astrobiología (CSIC-INTA), Ctra Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
e-mail: lrodriguez@cab.inta-csic.es
2
INAF-Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Florence, Italy
3
Dipartimento di Chimica “Giacomo Ciamician”, Universitá di Bologna, via F. Selmi 2, 40126 Bologna, Italy
4
Star and Planet Formation Laboratory, Cluster for Pioneering Research, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
5
Observatorio de Yebes (IGN), Cerro de la Palera s/n, 19141 Guadalajara, Spain
6
Eureopean Southern Observatory, Alonso de Córdova 3107, Vitacura, 763 0355 Santiago, Chile
7
Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, 763 0355 Santiago, Chile
8
University of Maryland, College Park, ND 20742-2421, USA
9
Department of Physics, Astronomy and Geosciences, Towson University, MD 21252, USA
Received:
9
August
2021
Accepted:
13
September
2021
Context. Little is known about the chemistry of isocyanates (compounds with the functional group R-N=C=O) in the interstellar medium (ISM), as only four of them have been detected so far: isocyanate radical (NCO), isocyanic acid (HNCO), N-protonated isocyanic acid (H2NCO+), and methyl isocyanate (CH3NCO). The molecular cloud G+0.693-0.027, located in the Galactic Centre, represents an excellent candidate to search for new isocyanates since it exhibits high abundances of the simplest ones, HNCO and CH3NCO.
Aims. After CH3NCO, the next most complex isocyanates are ethyl isocyanate (C2H5NCO) and vinyl isocyanate (C2H3NCO). Their detection in the ISM would enhance our understanding of the formation of these compounds in space.
Methods. We have searched for C2H5NCO, H2NCO+, C2H3NCO, and cyanogen isocyanate (NCNCO) in a sensitive unbiased spectral survey carried out in the 2 mm and 7 mm radio windows using the IRAM 30m and Yebes 40m radio telescopes, respectively.
Results. We have detected C2H5NCO and H2NCO+ towards G+0.693-0.027 (the former for the first time in the ISM) with molecular abundances of (4.7–7.3) × 10−11 and (1.0–1.5) × 10−11, respectively. A ratio of CH3NCO/C2H5NCO = 8 ± 1 is obtained; therefore, the relative abundance determined for HNCO:CH3NCO:C2H5NCO is 1:1/55:1/447, which implies a decrease by more than one order of magnitude, going progressively from HNCO to CH3NCO and to C2H5NCO. This is similar to what has been found for alcohols and thiols, for example, and suggests that C2H5NCO is likely formed on the surface of dust grains. In addition, we have obtained column density ratios of HNCO/NCO > 269, HNCO/H2NCO+ ∼ 2100, and C2H3NCO/C2H5NCO < 4. A comparison of the methyl/ethyl ratios for isocyanates (-NCO), alcohols (-OH), formiates (HCOO-), nitriles (-CN), and thiols (-SH) is performed and shows that ethyl derivatives may be formed more efficiently for the N-bearing molecules than for the O- and S-bearing molecules.
Key words: astrochemistry / ISM: molecules / line: identification
© ESO 2021
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