Carbon Dioxide Dissociates To Yield Molecular Oxygen Directly

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 O_2. In the other, CO₂ forms a triangular intermediate and then linear COO before dissociating into C and O₂.