Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...510..784k&link_type=abstract
The Astrophysical Journal, Volume 510, Issue 2, pp. 784-788.
Astronomy and Astrophysics
Astronomy
8
Ism: Molecules, Molecular Processes
Scientific paper
The energetics of the atom neutral reaction C(^3P_j) + C_2HD to form C_3D/C_3H isomers are investigated by ab initio calculations. In cold molecular clouds, the computed reaction endothermicity of 5.8 kJ mol^-1 to yield the linear isomer l-C_3H indicates that the reaction energy cannot be covered by the reactants' averaged translational energy of about 0.08 kJ mol^-1. This suggests that only the deuterated linear isomer, l-C_3D, could be formed in these environments. In strong contrast, reaction pathways to form the cyclic isomers c-C_3D and c-C_3H are both exothermic and hence could take place. These findings should be considered in prospective astronomical surveys of the fractional abundances of l-C_3H versus l-C_3D observed toward molecular clouds, since our results suggest an enhanced deuterium enrichment of the linear isomer versus the cyclic one. In a warmer outflow of carbon stars, the reaction endothermicity to form l-C_3H could be provided by the enhanced averaged translational temperature of the reactants, and the isotopic enrichment is expected to be less pronounced compared to colder interstellar environments.
Head-Gordon Martin
Kaiser Ralf I.
Lee Yin-Tat
Ochsenfeld C.
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