J/A+A/587/L4 Methyl isocyanate in Orion (Cernicharo+, 2016)
A rigorous detection of interstellar CH3NCO:
An important missing species in astrochemical networks.
Cernicharo J., Kisiel Z., Tercero B., Kolesnikova L., Medvedev I.R.,
Lopez A., Fortman S., Winnewisser M., de Lucia F.C., Alonso J.L.,
Guillemin J.-C.
<Astron. Astrophys. 587, L4 (2016)>
=2016A&A...587L...4C 2016A&A...587L...4C (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Radio lines; Spectroscopy
Keywords: ISM: abundances - ISM: individual objects (Orion KL) -
ISM: molecules - methods: laboratory: molecular - molecular data -
ISM: clouds
Abstract:
The recent analysis of the composition of the frozen surface of comet
67P/Churyumov-Gerasimenko has revealed a significant number of complex
organic molecules. Methyl isocyanate (CH3NCO) is one of the more
abundant species detected on the comet surface. In this work we report
extensive characterization of its rotational spectrum resulting in a
list of 1269 confidently assigned laboratory lines and its detection
in space towards the Orion clouds where 399 lines of the molecule have
been unambiguously identified. We find that the limited mm-wave
laboratory data reported prior to our work require some revision. The
abundance of CH3NCO in Orion is only a factor of ten below those of
HNCO and CH3CN. Unlike the molecular abundances in the coma of
comets, which correlate with those of warm molecular clouds, molecular
abundances in the gas phase in Orion are only weakly correlated with
those measured on the comet surface. We also compare our abundances
wit those derived recently for this molecule towards Sgr B2 (Halfen et
al., 2015ApJ...812L...5H 2015ApJ...812L...5H). A more accurate abundance of CH3NCO is
provided for this cloud based on our extensive laboratory work.
Description:
Final results of the analysis of the laboratory rotational spectrum of
CH3NCO for use in astrophysical applications. 300K line list for the
reported CH3NCO rotational transitions in the standard of the SPCAT
program (including intensities and lower state energies). This line
list is also given in Table A.6 in the standard format of the JPL
catalog (Pickett et al., 1998, J. Quant. Spectr. Rad. Transf., 60,
883).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea6.dat 114 1269 Line list for CH3NCO
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Byte-by-byte Description of file: tablea6.dat
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Bytes Format Units Label Explanations
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3- 12 F10.3 MHz Freq Frequency
16- 21 F6.4 MHz e_Freq Error on frequency
23- 29 F7.4 --- Log(Int) Base 10 logarithm of the integrated intensity
in units of nm2 MHz at 300K
31 I1 --- DR Degrees of freedom in the rotational partition
function
34- 41 F8.4 cm-1 Elow Energy of the lower level
43- 44 I2 --- gupp Upper state degeneracy
51- 52 I2 --- TAG Species tag or molecular identifier
53- 55 I3 --- QNFMT Format of the quantum numbers
56- 57 I2 --- QN0a Quantum numbers for the upper state
58- 59 I2 --- QN0b Quantum numbers for the upper state
60- 61 I2 --- QN0c Quantum numbers for the upper state
62- 63 I2 --- QN0d Quantum numbers for the upper state
64- 65 I2 --- QN0e ? Quantum numbers for the upper state
68- 69 I2 --- QN1a Quantum numbers for the lower state
70- 71 I2 --- QN1b Quantum numbers for the lower state
72- 73 I2 --- QN1c Quantum numbers for the lower state
74- 75 I2 --- QN1d Quantum numbers for the lower state
76- 77 I2 --- QN1e ? Quantum numbers for the lower state
81-114 A34 --- Seq Sequence
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Acknowledgements:
J. Cernicharo, jose.cernicharo(at)csic.es
B. Tercero, b.tercero(at)icmm.csic.es
References:
Pickett, H. M. 1991, J. Mol. Spectrosc., 148, 371, SPFIT/SPCAT package
available at http://spec.jpl.nasa.gov
(End) Patricia Vannier [CDS] 08-Feb-2016