J/A+A/587/L4 Methyl isocyanate in Orion (Cernicharo+, 2016) ================================================================================ A rigorous detection of interstellar CH_3_NCO: 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. =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 (CH_3_NCO) 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 CH_3_NCO in Orion is only a factor of ten below those of HNCO and CH_3_CN. 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). A more accurate abundance of CH_3_NCO is provided for this cloud based on our extensive laboratory work. Description: Final results of the analysis of the laboratory rotational spectrum of CH_3_NCO for use in astrophysical applications. 300K line list for the reported CH_3_NCO 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: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file tablea6.dat 114 1269 Line list for CH_3_NCO -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea6.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- 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