CO{sub 2} FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE CO + OH PATHWAY
- Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, Glasgow, G4 ONG (United Kingdom)
- LERMA-LAMAp, Universite de Cergy-Pontoise, Observatoire de Paris, ENS, UPMC, UMR 8112 du CNRS, 5 mail Gay Lussac, 95000 Cergy Pontoise Cedex (France)
The formation of CO{sub 2} in quiescent regions of molecular clouds is not yet fully understood, despite CO{sub 2} having an abundance of around 10%-34% H{sub 2}O. We present a study of the formation of CO{sub 2} via the nonenergetic route CO + OH on nonporous H{sub 2}O and amorphous silicate surfaces. Our results are in the form of temperature-programmed desorption spectra of CO{sub 2} produced via two experimental routes: O{sub 2} + CO + H and O{sub 3} + CO + H. The maximum yield of CO{sub 2} is around 8% with respect to the starting quantity of CO, suggesting a barrier to CO + OH. The rate of reaction, based on modeling results, is 24 times slower than O{sub 2} + H. Our model suggests that competition between CO{sub 2} formation via CO + OH and other surface reactions of OH is a key factor in the low yields of CO{sub 2} obtained experimentally, with relative reaction rates of k{sub CO+H}<<k{sub CO+OH}< k{sub H{sub 2}O{sub 2}+H}< k{sub OH+H},k{sub O{sub 2}+H}. Astrophysically, the presence of CO{sub 2} in low A{sub V} regions of molecular clouds could be explained by the reaction CO + OH occurring concurrently with the formation of H{sub 2}O via the route OH + H.
- OSTI ID:
- 21578368
- Journal Information:
- Astrophysical Journal, Vol. 735, Issue 2; Other Information: DOI: 10.1088/0004-637X/735/2/121; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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