J/A+A/700/A238 Line list for minor acetylene isotopologs (Lee+, 2025)
Precision analysis of 12C/13C ratios in Orion IRc2 acetylene isotopologs
via χ2 fitting.
Lee M., Park J., Oh S., Cheoun M.-K., Park S.Y.
<Astron. Astrophys. 700, A238 (2025)>
=2025A&A...700A.238L 2025A&A...700A.238L (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics ; Interstellar medium ; Spectra, infrared
Keywords: astrochemistry - line: identification - ISM: abundances -
ISM: molecules - infrared: ISM
Abstract:
We present a detailed analysis of acetylene (C2H2) and its
isotopologs in the orion IRc2, focusing on the determination
of 12C/13C isotopic ratios using high-resolution infrared spectra
from SOFIA. By employing a robust χ2 fitting method, we
simultaneously determined the temperature and column density, achieving a
12C/13C 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 χ2 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 13C and deuterium substitution, enabling
accurate isotopologue detection in astrophysical environments. The
Python package (TOPSEGI) developed in this study facilitates efficient
χ2 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.
Description:
Line lists are provided for seven minor isotopologs of acetylene
(IDs 3-9; 13C2H2, D12C13CH, D13C12CH, C2D2,
13C2HD, 12CCD2, and 13C2D2) for the nu5 bending
mode. The rotational and centrifugal distortion constants for the
upper level were estimated by scaling B3LYP-calculated values based on
structural similarity with isotopolog IDs 0, 1, and 2 (C2H2,
13CCH2, C2HD) corresponding to groups (3, 6, 9), (8), and (4, 5,
7), respectively. The data for IDs 0-2 were taken from the HITRAN
database. In addition, line intensities were computed assuming local
thermodynamic equilibrium (LTE) and normalized. Each file includes
line center wavenumber, line intensity, Einstein A-coefficient, lower
state energy, lower rotational quantum number, upper state statistical
weight, and lower state statistical weight. Furthermore, each dataset
(tablef2.dat to tablef8.dat) corresponds to Tables F.2 to F.8
in the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablef2.dat 50 150 13C2H2 line list of the ν5 band
for each acetylene isotopolog
tablef3.dat 50 150 D12C13CH line list of the ν5 band
for each acetylene isotopolog
tablef4.dat 50 150 D13C12CH line list of the ν5 band
for each acetylene isotopolog
tablef5.dat 50 150 C2D2 line list of the ν5 band
for each acetylene isotopolog
tablef6.dat 50 150 13C2HD line list of the ν5 band
for each acetylene isotopolog
tablef7.dat 50 150 13^CCD2 line list of the ν5 band
for each acetylene isotopolog
tablef8.dat 50 150 13C2D2 line list of the ν5 band
for each acetylene isotopolog
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Byte-by-byte Description of file: tablef?.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 cm-1 nu Lcenter wavenumber
11- 19 E9.3 cm/mol S Line intensity
21- 25 F5.3 s-1 A Einstein A-coefficient
27- 35 F9.4 cm-1 E" Lower state energy
37 A1 --- Branch P-, Q-, and R-branches
39- 40 I2 --- J" Lower rotational quantum number
42- 45 I4 --- g' Upper state statistical weight
47- 50 I4 --- g" Lower state statistical weight
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Acknowledgements:
Minkyu Lee, rkftor28gh(at)gmail.com
(End) M. Lee [Soongsil Univ. and OMEG Inst, Korea], P. Vannier [CDS] 09-Jul-2025