期刊
ASTROPHYSICAL JOURNAL
卷 735, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/735/2/121
关键词
astrochemistry; ISM: molecules; methods: laboratory
资金
- Leverhulme Trust
- Scottish International Education Trust
- University of Strathclyde
- Scottish Universities Physics Alliance
- European Community [238258]
- CNRS
- Conseil Regional d'Ile de France [I-07-597R]
- Conseil General du Val d'Oise
- Agence Nationale de Recherche [ANR07-BLAN-0129]
- EPSRC [EP/E022413/1] Funding Source: UKRI
- STFC [ST/G004307/1] Funding Source: UKRI
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 nonenergetic route CO + OH on nonporous H2O and amorphous silicate surfaces. Our results are in the form of temperature-programmed desorption spectra of CO2 produced via two experimental routes: O-2 + CO + H and O-3 + 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 modeling results, is 24 times slower than O-2 + 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 of k(CO+H) << 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.
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