Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 469, Issue 2, Pages 2219-2229Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stx890
Keywords
astrochemistry; molecular processes; techniques: spectroscopic; ISM: individual objects: IRAS 16293-2422; ISM: molecules
Categories
Funding
- European Union A-ERC [291141 CHEMPLAN]
- Netherlands Research School for Astronomy (NOVA)
- Royal Netherlands Academy of Arts and Sciences (KNAW)
- NOVA grant
- NWO (Netherlands Organisation for Scientific Research) grant
- STFC [ST/M001334/1]
- Lundbeck Foundation Group Leader Fellowship
- ERC under European Union's Horizon research and innovation programme through ERC [S4F, 646908]
- Danish National Research Foundation
- STFC [ST/M001334/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/M001334/1] Funding Source: researchfish
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Methyl isocyanate (CH3NCO) belongs to a select group of interstellar molecules considered to be relevant precursors in the formation of larger organic compounds, including those with peptide bonds. The molecule has only been detected in a couple of high-mass protostars and potentially on comets. A formation route on icy grains has been postulated for this molecule but experimental evidence is lacking. Here we extend the range of environments where methyl isocyanate is found and unambiguously identify CH3NCO through the detection of 43 unblended transitions in the ALMA Protostellar Interferometric Line Survey (PILS) of the low-mass solar-type protostellar binary IRAS 16293-2422. The molecule is detected towards both components of the binary with a ratio HNCO/CH3NCO similar to 4-12. The isomers CH3CNO and CH3OCN are not identified, resulting in upper abundance ratios of CH3NCO/CH3CNO > 100 and CH3NCO/CH3OCN > 10. The resulting abundance ratios compare well with those found for related N-containing species towards high-mass protostars. To constrain its formation, a set of cryogenic UHV experiments is performed. VUV irradiation of CH4:HNCO mixtures at 20 K strongly indicate that methyl isocyanate can be formed in the solid state through CH3 and (H)NCO recombinations. Combined with gas-grain models that include this reaction, the solid-state route is found to be a plausible scenario to explain the methyl isocyanate abundances found in IRAS 16293-2422.
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