Isotopic fractionation in the formation of ozone and of carbon dioxide

An explanation is proposed for the observed enrichment of the symmetric isomer OXO of heavy ozone (X being used to denote a heavy O atom). This is that the energized complex may undergo a flip in which one of the end atoms ceases to be effectively bound to the central atom and becomes effectively bound to the other end atom. The measured [OXO]:[OOX] ratio is reproduced if the flip frequency is the same as the dissociation frequency. Calculations are carried out on the variation of the enhancement with the ambient gas density. It is reasoned that the enhancement observed in the stratosphere is that arising in termolecular association and that the lower values obtained in laboratory experiments are artifacts. The measured isotopic enrichment of carbon dioxide may arise from termolecular association O+CO+CO→CO2+CO, from enriched OXO* that is generated in another association process or from both. The apparent scatter in the results is much greater than would be expected from the precision of the measurements. It is suggested that this may be an artifact (similar in origin to those for ozone).