J/A+A/628/A53ivo://CDS.VizieR/J/A+A/628/A53doi:10.26093/cds/vizier.36280053CDSGiuliano B.M.Bizzocchi L.Pietropolli Charmet A.Arenas B.E.,Steber A.L.Schnell M.Caselli P.Harris B.J.Pate B.H.,Guillemin J.-C.Belloche A.2019-08-21T11:01:17Z2019-08-06T08:43:18ZCDS support team

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

cds-question@unistra.fratomic-physicsOrganic ring compounds play a key role in terrestrial biochemistry, and they were also most likely pivotal ingredients in Earth's prebiotic chemistry. The five-membered ring imidazole, c-C3N2H4, is a substructure of fundamental biological molecules such as the purine nucleobases and the amino acid histidine. An unsuccessful search for imidazole in a sample of cold-core clouds and massive star-forming regions was performed almost 40 years ago. At that time, the spectroscopic knowledge of this species was scarce: the existing laboratory study was limited to the centimetre-wave region, and the precision of the rest frequencies in the millimetre regime was not adequate. The goal of the present work is to perform a comprehensive investigation of the rotational Spectrum of imidazole in its ground vibrational state from the microwave region to the 1mm wavelength regime. The rotational spectrum of imidazole was recorded in selected frequency regions from 2 to 295GHz. These intervals were covered using various broadband spectrometers developed at DESY (Hamburg) and at the University of Virginia. High-level ab initio calculations were performed to obtain reliable estimates of the quartic and sextic centrifugal distortion constants. We used the EMoCA imaging spectral line survey to search for imidazole towards the hot molecular core Sgr B2(N2). About 700 rotational transitions spanning a J interval from 0 to 59 and Kc interval from 0 to 30 were analysed using the Watson S-reduced Hamiltonian. These new data allowed the determination of a much extended set of spectroscopic parameters for imidazole in its vibrational ground state. The improved spectral data allow us to set an upper limit to the column density of imidazole in SgrB2(N2). Its non-detection implies that it is at least 3400 times less abundant than ethyl cyanide in this source. With the new set of spectroscopic constants, it has been possible to compute reliable rest frequencies at millimetre wavelengths. We suggest a search for imidazole towards TMC-1, where the aromatic molecule benzonitrile was recently detected.2019A&A...628A..53Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/628/A53CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/628/A53https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/628/A53http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/628/A53https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/628/A53https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/628/A53http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/628/A53GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/628/A53/table1Assignments, measured line positions and least-squares residuals for the analysed transitions of imidazole with hyperfine structurerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ1Upper state Jmeta.noteintKa1Upper state Kaphys.mol.qnintKc1Upper state Kcphys.mol.qnintF11Upper state F1phys.mol.qnintF1Upper state Fphys.mol.qnintJ0Lower state Jmeta.noteintKa0Lower state Kaphys.mol.qnintKc0Lower state Kcphys.mol.qnintF10Lower state F1phys.mol.qnintF0Lower state Fphys.mol.qnintObserved? Measured line positionMHzem.freqdoublenullableO-C? Least-squares residual (fit I)MHzstat.fit.residualdoublenullableWeight? Relative weight in a line blendstat.weight;phys.atmol.weight;spect.linefloatnullableJ/A+A/628/A53/imidaCDMS-like file for imidazole without hyperfine structureF0? Lower state Fphys.mol.qnintnullableKa0Lower state Kaphys.mol.qnintKc0Lower state Kcphys.mol.qnintF10? Lower state F1phys.mol.qnintnullableJ1Upper state Jmeta.noteintKa1Upper state Kaphys.mol.qnintKc1Upper state Kcphys.mol.qnintF11? Upper state F1phys.mol.qnintnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFreqFrequency of the lineMHzem.freqdoublee_Frequncertainty on the lineMHzstat.errorfloatlogIntbase 10 logarithm of the integrated intensity at 300Klog(nm**2.MHz)spect.line.intensityfloatdof[3] Degree of freedom in the rotational partition function (1)stat.fit.dofintE0Lower state energycm**-1phys.energy;phys.atmol.leveldoublegupUpper state degeneracyphys.electron.degenintMolTag[686011] Molecule tag (2)meta.noteintCode[403-405] Coding of the quantum numbersmeta.codeintJ0Lower state Jmeta.noteintF1? Upper state Fphys.mol.qnintnullableJ/A+A/628/A53/table2Assignments, measured line positions and least-squares residuals for the analysed transitions of imidazole without hyperfine structurerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ1Upper state Jmeta.noteintKa1Upper state Kaphys.mol.qnintKc1Upper state Kcphys.mol.qnintJ0Lower state Jmeta.noteintKa0Lower state Kaphys.mol.qnintKc0Lower state Kcphys.mol.qnintObserved? Measured line positionMHzem.freqdoublenullableO-C? Least-squares residual (fit I)MHzstat.fit.residualdoublenullableWeight? Relative weight in a line blendstat.weight;phys.atmol.weight;spect.linefloatnullableJ/A+A/628/A53/imidahfsCDMS-like file for imidazole with hyperfine structurerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFreqFrequency of the lineMHzem.freqdoublee_Frequncertainty on the lineMHzstat.errorfloatlogIntbase 10 logarithm of the integrated intensity at 300Klog(nm**2.MHz)spect.line.intensityfloatdof[3] Degree of freedom in the rotational partition function (1)stat.fit.dofintE0Lower state energycm**-1phys.energy;phys.atmol.leveldoublegupUpper state degeneracyphys.electron.degenintMolTag[686011] Molecule tag (2)meta.noteintCode[403-405] Coding of the quantum numbersmeta.codeintJ0Lower state Jmeta.noteintKa0Lower state Kaphys.mol.qnintKc0Lower state Kcphys.mol.qnintF10? Lower state F1phys.mol.qnintnullableF0? Lower state Fphys.mol.qnintnullableJ1Upper state Jmeta.noteintKa1Upper state Kaphys.mol.qnintKc1Upper state Kcphys.mol.qnintF11? Upper state F1phys.mol.qnintnullableF1? Upper state Fphys.mol.qnintnullable