CO2 formation in quiescent clouds: AN experimental study of the CO + OH pathway

J. A. Noble, F. Dulieu, E. Congiu, H. J. Fraser

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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: O2 + CO+ H and O3 + CO+ H. The maximum yield of CO 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 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 of . 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.

Original languageEnglish
Article number121
JournalAstrophysical Journal
Issue number2
StatePublished - Jul 10 2011
Externally publishedYes


  • ISM: molecules
  • astrochemistry
  • methods: laboratory


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