Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2011-03-31
ApJ, 2011, 735, 121
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
13 pages, 3 figures, 2 tables, accepted for publication in ApJ
Scientific paper
10.1088/0004-637X/735/2/121
The formation of CO2 in quiescent regions of molecular clouds is not yet fully understood, despite CO2 having an abundance of around 10-34 % H2O. We present a study of the formation of CO2 via the non-energetic route CO + OH on non-porous H2O and amorphous silicate surfaces. Our results are in the form of temperature-programmed desorption spectra of CO2 produced via two experimental routes: O2 + CO + H and O3 + CO + H. The maximum yield of CO2 is around 8 % with respect to the starting quantity of CO, suggesting a barrier to CO + OH. The rate of reaction, based on modelling results, is 24 times slower than O2 + H. Our model suggests that competition between CO2 formation via CO + OH and other surface reactions of OH is a key factor in the low yields of CO2 obtained experimentally, with relative reaction rates k(CO+H) \ll k(CO+OH) < k(H2O2+H) < k(OH+H), k(O2+H). Astrophysically, the presence of CO2 in low AV regions of molecular clouds could be explained by the reaction CO + OH occurring concurrently with the formation of H2O via the route OH + H.
Congiu Emanuele
Dulieu Francois
Fraser Helen Jane
Noble Jennifer Anna
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