J/A+A/666/A50ivo://CDS.VizieR/J/A+A/666/A50doi:10.26093/cds/vizier.36660050CDSVavra K.Kolesnikova L.Belloche A.Garrod R.T.Koucky J.Uhlikova T.,Lukova K.Guillemin J.-C.Kania P.Muller H.S.P.Menten K.M.Urban S.2022-10-12T12:10:55Z2022-10-04T09:40:09ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fratomic-physicsinterstellar-mediumspectroscopyThe interstellar detections of isocyanic acid (HNCO), methyl isocyanate (CH_3_NCO), and very recently also ethyl isocyanate (C_2_H_5_NCO) invite the question of whether or not vinyl isocyanate (C_2_H_3_NCO) can be detected in the interstellar medium. There are only low-frequency spectroscopic data (<40GHz) available for this species in the literature, which makes predictions at higher frequencies rather uncertain, which in turn hampers searches for this molecule in space using millimeter (mm) wave astronomy. The aim of the present study is on one hand to extend the laboratory rotational spectrum of vinyl isocyanate to the mm wave region and on the other to search, for the first time, for its presence in the high-mass star-forming region Sgr B2, where other isocyanates and a plethora of complex organic molecules are observed. We recorded the pure rotational spectrum of vinyl isocyanate in the frequency regions 127.5-218 and 285-330GHz using the Prague mm wave spectrometer. The spectral analysis was supported by high-level quantum-chemical calculations. On the astronomy side, we assumed local thermodynamic equilibrium to compute synthetic spectra of vinyl isocyanate and to search for it in the ReMoCA survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming protocluster Sgr B2(N). Additionally, we searched for the related molecule ethyl isocyanate in the same source. Accurate values for the rotational and centrifugal distortion constants are reported for the ground vibrational states of trans and cis vinyl isocyanate from the analysis of more than 1000 transitions. We report nondetections of vinyl and ethyl isocyanate toward the main hot core of Sgr B2(N). We find that vinyl and ethyl isocyanate are at least 11 and 3 times less abundant than methyl isocyanate in this source, respectively. Although the precise formation mechanism of interstellar methyl isocyanate itself remains uncertain, we infer from existing astrochemical models that our observational upper limit for the CH_3_NCO:C_2_H_5_NCO ratio in Sgr B2(N) is consistent with ethyl isocyanate being formed on dust grains via the abstraction or photodissociation of an H atom from methyl isocyanate, followed by the addition of a methyl radical. The dominance of such a process for ethyl isocyanate production, combined with the absence of an analogous mechanism for vinyl isocyanate, would indicate that the ratio C_2_H_3_NCO:C_2_H_5_NCO should be less than unity. Even though vinyl isocyanate was not detected toward Sgr B2(N), the results of this work represent a significant improvement on previous low-frequency studies and will help the astronomical community to continue searching for this species in the Universe.2022A&A...666A..50Vhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/666/A50CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/666/A50https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/666/A50http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/666/A50https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/666/A50https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/666/A50http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/666/A50GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/666/A50/tablea2List of the measured transitions of trans vinyl isocyanateJ'Upper state J quantum numberphys.atmol.configurationintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintKa'Upper state Ka quantum numberphys.atmol.qnintKc'Upper state Kc quantum numberphys.atmol.qnintJ"Lower state J quantum numberphys.atmol.configurationintKa"Lower state Ka quantum numberphys.atmol.qnintKc"Lower state Kc quantum numberphys.atmol.qnintFreqObsObserved transition frequencyMHzem.freqdoubleO-CObserved minus calculated frequencyMHzem.freq;stat.fit.omcfloate_FreqExperimental uncertaintyMHzstat.errorfloat(O-C)b? Observed minus calculated frequency for blendsMHzem.freq;stat.fit.omcfloatnullablewb? Weight of the components of the blendsphys.atmol.weightfloatnullableNotesSource of the data (G1)meta.notecharJ/A+A/666/A50/tablea3List of the measured transitions of cis vinyl isocyanaterecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ'Upper state J quantum numberphys.atmol.configurationintKa'Upper state Ka quantum numberphys.atmol.qnintKc'Upper state Kc quantum numberphys.atmol.qnintJ"Lower state J quantum numberphys.atmol.configurationintKa"Lower state Ka quantum numberphys.atmol.qnintKc"Lower state Kc quantum numberphys.atmol.qnintFreqObsObserved transition frequencyMHzem.freqdoubleO-CObserved minus calculated frequencyMHzem.freq;stat.fit.omcfloate_FreqExperimental uncertaintyMHzstat.errorfloat(O-C)b? Observed minus calculated frequency for blendsMHzem.freq;stat.fit.omcfloatnullablewb? Weight of the components of the blendsphys.atmol.weightfloatnullableNotesSource of the data (G1)meta.notecharJ/A+A/666/A50/tablea5JPL/CDMS catalog line list for trans vinyl isocyanateJ"Lower state J quantum numberphys.atmol.configurationcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFreqFrequency (1)MHzem.freqdoublee_FreqUncertainty of the frequencyMHzstat.errorfloatlog(Int)Base 10 logarithm of the integrated intensity in units of nm2 MHz at 300Klog(nm**2.MHz)spect.line.intensityfloatDRDegrees of freedom in the rotational partition functionstat.fit.dofintElowEnergy of the lower levelcm**-1phys.energy;phys.atmol.leveldoubleguppUpper state degeneracyphys.electron.degenintTAGSpecies tag or molecular identifiermeta.codeintQNFMTFormat of the quantum numbersphys.atmol.qnintJ'Upper state J quantum numberphys.atmol.configurationcharKa'Upper state Ka quantum numberphys.atmol.qnintKc'Upper state Kc quantum numberphys.atmol.qncharKa"Lower state Ka quantum numberphys.atmol.qnintKc"Lower state Kc quantum numberphys.atmol.qncharJ/A+A/666/A50/tablea6JPL/CDMS catalog line list for cis vinyl isocyanateTAGSpecies tag or molecular identifiermeta.codeintQNFMTFormat of the quantum numbersphys.atmol.qnintJ'Upper state J quantum numberphys.atmol.configurationintKa'Upper state Ka quantum numberphys.atmol.qnintKc'Upper state Kc quantum numberphys.atmol.qnintJ"Lower state J quantum numberphys.atmol.configurationintKa"Lower state Ka quantum numberphys.atmol.qnintKc"Lower state Kc quantum numberphys.atmol.qnintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFreqFrequency (2)MHzem.freqdoublee_FreqUncertainty of the frequencyMHzstat.errorfloatlog(Int)Base 10 logarithm of the integrated intensity in units of nm2 MHz at 300Klog(nm**2.MHz)spect.line.intensityfloatDRDegrees of freedom in the rotational partition functionstat.fit.dofintElowEnergy of the lower levelcm**-1phys.energy;phys.atmol.leveldoubleguppUpper state degeneracyphys.electron.degenint