The non-mass-dependent oxygen isotope effect in the electrodissociation of carbon dioxide: A step toward understanding NoMaD chemistry

A non-mass dependent (NoMaD) oxygen isotope effect is demonstrated in the dissociation of CO ₂ similar to that observed in the electrosynthesis of ozone. The molecular oxygen produced carries the signature of two separate isotopic fractionation processes; a mass-dependent fractionation probably due to CO ₂ + O isotopic exchange, and a secondary NoMaD fractionation ( δ¹⁷O = 0.97 ± 0.09 δ¹⁸O, with the O ₂ depleted in ¹⁷O and ¹⁸O). It is suggested that the effect is due to either the formation or relaxation of ozone in an excited electronic state. This represents the latest advance in the understanding of chemical NoMaD effects which may be essential to the explanation of non-mass-dependent fractionations observed in meteorites.