J/A+A/700/A238ivo://CDS.VizieR/J/A+A/700/A238doi:10.26093/cds/vizier/bc-nw/lcdiCDSLee M.Park J.Oh S.Cheoun M.-K.Park S.Y.2026-08-03T06:56:36Z2025-08-26T08:47:42ZCDS support team

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

cds-question@unistra.fratomic-physicsinterstellar-mediuminfrared-astronomyspectroscopyWe present a detailed analysis of acetylene (C_2_H_2_) and its isotopologs in the orion IRc2, focusing on the determination of ^12^C/^13^C isotopic ratios using high-resolution infrared spectra from SOFIA. By employing a robust {chi}^2^ fitting method, we simultaneously determined the temperature and column density, achieving a ^12^C/^13^C ratio of 18.73^+1.54^_-1.47_ for the blue clump and 15.07^+1.61^_-1.60_ for the red clump. These results revealed significant discrepancies with the traditional rotational diagram method, which overestimated the ratios by 12.1% and 23.9%, respectively. Our {chi}^2^ approach also reduced uncertainties by up to 75%, providing more precise and reliable isotopic ratios. additionally, we extended the analysis to isotopologs not covered in hitran, calculating vibrational and rotational constants through quantum chemical calculations. This allowed us to model subtle isotopic shifts induced by ^13^C and deuterium substitution, enabling accurate isotopologue detection in astrophysical environments. The Python package (TOPSEGI) developed in this study facilitates efficient {chi}^2^ fitting and isotopic ratio analysis, making it a valuable tool for future high-resolution observations. This work highlights the critical role of advanced spectral models and fitting techniques in understanding isotopic fractionation and the chemical evolution of interstellar matter.2025A&A...700A.238Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/700/A238CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/700/A238https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/700/A238http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/700/A238https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/700/A238https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/700/A238http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/700/A238GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfrareddefaultJ/A+A/700/A238/tablef2^13^C_2_H_2_ line list of the {nu}_5_ band for each acetylene isotopologrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintnuLcenter wavenumbercm**-1em.freqdoubleSLine intensitycm/molspect.line.intensitydoubleAEinstein A-coefficients**-1phys.atmol.transProbfloatE"Lower state energycm**-1phys.energy;phys.atmol.leveldoubleBranchP-, Q-, and R-branchesmeta.notecharJ"Lower rotational quantum numberphys.mol.qn;phys.mol.rotation;stat.minintg'Upper state statistical weightstat.weight;phys.atmol.configurationintg"Lower state statistical weightstat.weight;phys.atmol.configurationintJ/A+A/700/A238/tablef3D^12^C^13^CH line list of the {nu}_5_ band for each acetylene isotopologrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintnuLcenter wavenumbercm**-1em.freqdoubleSLine intensitycm/molspect.line.intensitydoubleAEinstein A-coefficients**-1phys.atmol.transProbfloatE"Lower state energycm**-1phys.energy;phys.atmol.leveldoubleBranchP-, Q-, and R-branchesmeta.notecharJ"Lower rotational quantum numberphys.mol.qn;phys.mol.rotation;stat.minintg'Upper state statistical weightstat.weight;phys.atmol.configurationintg"Lower state statistical weightstat.weight;phys.atmol.configurationintJ/A+A/700/A238/tablef4D^13^C^12^CH line list of the {nu}_5_ band for each acetylene isotopologrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintnuLcenter wavenumbercm**-1em.freqdoubleSLine intensitycm/molspect.line.intensitydoubleAEinstein A-coefficients**-1phys.atmol.transProbfloatE"Lower state energycm**-1phys.energy;phys.atmol.leveldoubleBranchP-, Q-, and R-branchesmeta.notecharJ"Lower rotational quantum numberphys.mol.qn;phys.mol.rotation;stat.minintg'Upper state statistical weightstat.weight;phys.atmol.configurationintg"Lower state statistical weightstat.weight;phys.atmol.configurationintJ/A+A/700/A238/tablef5C_2_D_2_ line list of the {nu}_5_ band for each acetylene isotopologrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintnuLcenter wavenumbercm**-1em.freqdoubleSLine intensitycm/molspect.line.intensitydoubleAEinstein A-coefficients**-1phys.atmol.transProbfloatE"Lower state energycm**-1phys.energy;phys.atmol.leveldoubleBranchP-, Q-, and R-branchesmeta.notecharJ"Lower rotational quantum numberphys.mol.qn;phys.mol.rotation;stat.minintg'Upper state statistical weightstat.weight;phys.atmol.configurationintg"Lower state statistical weightstat.weight;phys.atmol.configurationintJ/A+A/700/A238/tablef6^13^C_2_HD line list of the {nu}_5_ band for each acetylene isotopologrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintnuLcenter wavenumbercm**-1em.freqdoubleSLine intensitycm/molspect.line.intensitydoubleAEinstein A-coefficients**-1phys.atmol.transProbfloatE"Lower state energycm**-1phys.energy;phys.atmol.leveldoubleBranchP-, Q-, and R-branchesmeta.notecharJ"Lower rotational quantum numberphys.mol.qn;phys.mol.rotation;stat.minintg'Upper state statistical weightstat.weight;phys.atmol.configurationintg"Lower state statistical weightstat.weight;phys.atmol.configurationintJ/A+A/700/A238/tablef713^CCD_2_ line list of the {nu}_5_ band for each acetylene isotopologrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintnuLcenter wavenumbercm**-1em.freqdoubleSLine intensitycm/molspect.line.intensitydoubleAEinstein A-coefficients**-1phys.atmol.transProbfloatE"Lower state energycm**-1phys.energy;phys.atmol.leveldoubleBranchP-, Q-, and R-branchesmeta.notecharJ"Lower rotational quantum numberphys.mol.qn;phys.mol.rotation;stat.minintg'Upper state statistical weightstat.weight;phys.atmol.configurationintg"Lower state statistical weightstat.weight;phys.atmol.configurationintJ/A+A/700/A238/tablef8^13^C_2_D_2_ line list of the {nu}_5_ band for each acetylene isotopologrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintnuLcenter wavenumbercm**-1em.freqdoubleSLine intensitycm/molspect.line.intensitydoubleAEinstein A-coefficients**-1phys.atmol.transProbfloatE"Lower state energycm**-1phys.energy;phys.atmol.leveldoubleBranchP-, Q-, and R-branchesmeta.notecharJ"Lower rotational quantum numberphys.mol.qn;phys.mol.rotation;stat.minintg'Upper state statistical weightstat.weight;phys.atmol.configurationintg"Lower state statistical weightstat.weight;phys.atmol.configurationint