CARBON ISOTOPE AND ISOTOPOMER FRACTIONATION IN COLD DENSE CLOUD CORES

Journal Article · Sun Apr 10 00:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/731/1/38· OSTI ID:21578430

Furuya, Kenji; Aikawa, Yuri ^[1]; Sakai, Nami; Yamamoto, Satoshi ^[2]

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1. Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan)
2. Department of Physics and Research Center for the Early Universe, University of Tokyo, Bunkyo-ku, Tokyo 113-003 (Japan)

We construct a gas-grain chemical network model which includes carbon isotopes ({sup 12}C and {sup 13}C) with an emphasis on isotopomer-exchange reactions. Temporal variations of molecular abundances, the carbon isotope ratios ({sup 12}CX/{sup 13}CX), and the isotopomer ratios ({sup 12}C{sup 13}CX/{sup 13}C{sup 12}CX) of CCH and CCS in cold dense cloud cores are investigated by numerical calculations. We confirm that the isotope ratios of molecules, both in the gas phase and grain surfaces, are significantly different depending on whether the molecule is formed from the carbon atom (ion) or the CO molecule. Molecules formed from carbon atoms have CX/{sup 13}CX ratios greater than the elemental abundance ratio of [{sup 12}C/{sup 13}C]. On the other hand, molecules formed from CO molecules have CX/{sup 13}CX ratios smaller than the [{sup 12}C/{sup 13}C] ratio. We reproduce the observed C{sup 13}CH/{sup 13}CCH ratio in TMC-1, if the isotopomer-exchange reaction, {sup 13}CCH + H {r_reversible} C{sup 13}CH + H + 8.1 K, proceeds with the forward rate coefficient k{sub f} > 10{sup -11} cm{sup 3} s{sup -1}. However, the C{sup 13}CS/{sup 13}CCS ratio is lower than that observed in TMC-1. We then assume the isotopomer-exchange reaction catalyzed by the H atom, {sup 13}CCS + H {r_reversible} C{sup 13}CS + H + 17.4 K. In the model with this reaction, we reproduce the observed C{sup 13}CS/{sup 13}CCS, CCS/C{sup 13}CS, and CCS/{sup 13}CCS ratios simultaneously.

• OSTI ID: 21578430
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 731; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABUNDANCE
CARBON 12
CARBON 13
CARBON COMPOUNDS
CARBON ISOTOPES
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
CLOUDS
DIMENSIONLESS NUMBERS
ELEMENT ABUNDANCE
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FRACTIONATION
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
NUCLEI
OXIDES
OXYGEN COMPOUNDS
SEPARATION PROCESSES
STABLE ISOTOPES