AN APPARENT NEW ISOTOPE EFFECT IN A MOLECULAR DECOMPOSITION AND IMPLICATIONS FOR NATURE

The isotopic fractionation resulting from thermal ozone decomposition has been measured. The product O2 from gas phase thermal decomposition is equally enriched in 17O and 18O with respect to precursor O3. The effect is not due to O+O2+M reaction, which is the source of another reported mass-independent isotope effect. Previous experiments have shown that visible light O3 decomposition produces isotopically light O2, thus, it appears that the source of the anomalous isotopic fractionation observed in thermal decomposition is the collisional decomposition process. This may then represent a new type of isotope effect not accounted for by theory. The possible consequence for observation in nature is discussed. © 1990.