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Evidence for direct molecular oxygen production in CO2 photodissociation

Science  03 Oct 2014:
Vol. 346, Issue 6205, pp. 61-64
DOI: 10.1126/science.1257156

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Illuminating oxygen out of carbon dioxide

It has long been known that high-energy ultraviolet light can split carbon dioxide into CO and O fragments. Lu et al. have now uncovered a parallel pathway that appears to yield C and O2 instead (see the Perspective by Suits and Parker). By precisely measuring the energy and trajectory of the carbon fragment after CO2 irradiation, O2 formation could be inferred. The results introduce a potential mechanism for abiotic oxygen production in CO2-heavy atmospheres of other planets.

Science, this issue p. 61; see also p.30

Abstract

Photodissociation of carbon dioxide (CO2) has long been assumed to proceed exclusively to carbon monoxide (CO) and oxygen atom (O) primary products. However, recent theoretical calculations suggested that an exit channel to produce C + O2 should also be energetically accessible. Here we report the direct experimental evidence for the C + O2 channel in CO2 photodissociation near the energetic threshold of the C(3P) + O2(X3Σg) channel with a yield of 5 ± 2% using vacuum ultraviolet laser pump-probe spectroscopy and velocity-map imaging detection of the C(3PJ) product between 101.5 and 107.2 nanometers. Our results may have implications for nonbiological oxygen production in CO2-heavy atmospheres.

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