Carbon Dioxide Dissociates To Yield Molecular Oxygen Directly | Chemical & Engineering News
Volume 92 Issue 40 | p. 35 | Concentrates
Issue Date: October 6, 2014

Carbon Dioxide Dissociates To Yield Molecular Oxygen Directly

Finding suggests that atmospheric oxygen may not always be a sign of life
Department: Science & Technology
News Channels: Biological SCENE, Environmental SCENE
Keywords: carbon dioxide, oxygen, extraterrestrial life, astrochemistry, astrobiology

Studies of light-driven carbon dioxide dissociation have tended to focus exclusively on the products CO and O. But new evidence reveals that the molecule can also break down into C and O2, report University of California, Davis, researchers (Science 2014, DOI: 10.1126/science.1257156). The results confirm theoretical predictions and indicate that physical processes can produce more O2 in planetary atmospheres than previously realized, suggesting that the presence of O2 may not automatically be a sign of life on other worlds. The work “will have great impact in astrobiology because molecular oxygen is considered a pretty solid biomarker,” NASA’s Louis J. Allamandola comments. The UC Davis researchers, led by Cheuk-Yiu Ng and William M. Jackson, studied CO2 photodissociation using vacuum ultraviolet laser pump-probe spectroscopy and found that about 5% of CO2 photodissociation yields C and O2 as primary products. They propose two possible reaction pathways for O2 production. In one, an oxygen atom partially dissociates from CO2 and then roams around the remaining CO before reacting to form C and O2. In the other, CO2 forms a triangular intermediate and then linear COO before dissociating into C and O2.

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Proposed pathways for CO2 photodissociation into C and O2 (C is gray, O is red) include a roaming mechanism in which an oxygen atom partially dissociates (top) or formation of triangular and linear intermediates (bottom).Proposed pathways for CO2 photodissociation into C and O2 (C is gray, O is red) include a roaming mechanism in which an oxygen atom partially dissociates (top) or formation of triangular and linear intermediates (bottom).
Proposed pathway for CO2 photodissociation into C and O2 (C is gray, O is red) that includes a roaming mechanism in which an oxygen atom partially dissociates (top) or formation of triangular and linear intermediates (bottom).
 
Proposed pathways for CO2 photodissociation into C and O2 (C is gray, O is red) include a roaming mechanism in which an oxygen atom partially dissociates (top) or formation of triangular and linear intermediates (bottom).Proposed pathways for CO2 photodissociation into C and O2 (C is gray, O is red) include a roaming mechanism in which an oxygen atom partially dissociates (top) or formation of triangular and linear intermediates (bottom).
 
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