J/A+A/602/A34ivo://CDS.VizieR/J/A+A/602/A34doi:10.26093/cds/vizier.36020034CDSBizzocchi L.Lattanzi V.Laas J.Spezzano S.Giuliano B.M.,Prudenzano D.Endres C.Sipilae O.Caselli P.2017-06-12T08:45:06Z2017-05-31T09:40:55ZCDS support team

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

cds-question@unistra.fratomic-physicsHOCO^+^ is a polar molecule that represents a useful proxy for its parent molecule CO2, which is not directly observable in the cold interstellar medium. This cation has been detected towards several lines of sight, including massive star forming regions, protostars, and cold cores. Despite the obvious astrochemical relevance, protonated CO2 and its deuterated variant, DOCO^+^, still lack an accurate spectroscopic characterisation. The aim of this work is to extend the study of the ground-state pure rotational spectra of HOCO^+^ and DOCO^+^ well into the sub-millimetre region. Ground-state transitions have been recorded in the laboratory using a frequency-modulation absorption spectrometer equipped with a free-space glow-discharge cell. The ions were produced in a low-density, magnetically confined plasma generated in a suitable gas mixture. The ground-state spectra of HOCO^+^ and DOCO^+^ have been investigated in the 213-967GHz frequency range; 94 new rotational transitions have been detected. Additionally, 46 line positions taken from the literature have been accurately remeasured. The newly measured lines have significantly enlarged the available data sets for HOCO^+^ and DOCO^+^, thus enabling the determination of highly accurate rotational and centrifugal distortion parameters. Our analysis shows that all HOCO^+^ lines with Ka>=3 are perturbed by a ro-vibrational interaction that couples the ground state with the v5=1 vibrationally excited state. This resonance has been explicitly treated in the analysis in order to obtain molecular constants with clear physical meaning. The improved sets of spectroscopic parameters provide enhanced lists of very accurate sub-millimetre rest frequencies of HOCO^+^ and DOCO2017A&A...602A..34Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/602/A34CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/602/A34https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/602/A34http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/602/A34https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/602/A34https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/602/A34http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/602/A34GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/602/A34/table1Assignments, measured line positions and least-squares residuals for the analysed transitions of HOCO+KaLower state Kaphys.mol.qnintKc? Lower state Kcphys.mol.qnintnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ'Upper state Jmeta.noteintKa'Upper state Kaphys.mol.qnintKc'? Upper state Kcphys.mol.qnintnullablen_Kc'[*] * for unresolved asymmetry doubletmeta.notecharJLower state Jphys.atmol.qnintn_Kc[*] * for unresolved asymmetry doubletmeta.notecharObsMeasured line positionMHzem.freqdoubleO-CfitI? Least-squares residual (fit I) (1)MHzstat.fit.residualfloatnullableO-CfitIILeast-squares residual (fit II)MHzstat.fit.residualfloatuncAssumed uncertaintyMHzstat.errorfloatRefReference (G1)meta.ref;pos.framecharJ/A+A/602/A34/table4Predicted rest frequencies, estimated accuracies and lines strenghts for the ground vibrational state of DOCO+recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ'Upper state Jmeta.noteintKa'Upper state Kaphys.mol.qnintKc'Upper state Kcphys.mol.qnintJLower state Jphys.atmol.qnintKaLower state Kaphys.mol.qnintKcLower state Kcphys.mol.qnintRestFreqRest frequencyMHzem.freqdoublee_RestFreqEstimated error on RestFreqkHzstat.errorintStrengthTransition strengthD**2spect.line.strength;phys.atmol.transitiondoubleEupperUpper state energycm**-1phys.energy;phys.atmol.levelfloatAcoeffEinstein's A coefficients**-1phys.atmol.transProbdoubleJ/A+A/602/A34/table2Assignments, measured line positions and least-squares residuals for the analysed transitions of DOCO+recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ'Upper state Jmeta.noteintKa'Upper state Kaphys.mol.qnintKc'? Upper state Kcphys.mol.qnintnullablen_Kc'[*] * for unresolved asymmetry doubletmeta.notecharJLower state Jphys.atmol.qnintKaLower state Kaphys.mol.qnintKc? Lower state Kcphys.mol.qnintnullablen_Kc[*] * for unresolved asymmetry doubletmeta.notecharObsMeasured line positionMHzem.freqdoubleO-CLeast-squares residualMHzstat.fit.residualfloatuncAssumed uncertaintyMHzstat.errorfloatRefReferencemeta.ref;pos.framecharJ/A+A/602/A34/table3Predicted rest frequencies, estimated accuracies and lines strenghts for the ground vibrational state of HOCO+recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ'Upper state Jmeta.noteintKa'Upper state Kaphys.mol.qnintKc'Upper state Kcphys.mol.qnintJLower state Jphys.atmol.qnintKaLower state Kaphys.mol.qnintKcLower state Kcphys.mol.qnintRestFreqRest frequencyMHzem.freqdoublee_RestFreqEstimated error on RestFreqkHzstat.errorintStrengthTransition strengthD**2spect.line.strength;phys.atmol.transitiondoubleEupperUpper state energycm**-1phys.energy;phys.atmol.levelfloatAcoeffEinstein's A coefficients**-1phys.atmol.transProbdouble