Anomalous enrichment of 17O and 13C in photodissociation products of CO2: Possible role of nuclear spin

Oxygen and carbon isotope fractionation associated with products (CO and O-2) of gas phase photodissociation of CO2 have been studied using photons from Hg lamp (184.9 nm) and Kr lamp (123.6 and 116.5 nm). In dissociation by Hg lamp photons both CO and O-2 are enriched in O-17 by about 81 parts per thousand compared to the estimate based on a kinetic model. Additionally, CO is enriched in C-13 by about 37 parts per thousand relative to the model composition. In contrast, in dissociation by higher energy Kr lamp photons no such anomaly was found in O-2. The observed isotopic enrichments in case of Hg lamp dissociation are proposed to be due to a hyperfine interaction between nuclear spin and electron spins or orbital motion causing enhanced dissociation of isotopologues of CO2 containing O-17 and C-13. The O-17 enrichment is higher than that of C-13 by a factor of 2.2 +/- 0.2 which can be explained by the known magnetic moment ratio of O-17 and C-13 due to differing nuclear spins and g-factors. These results have potential implications in studies of the planetary atmospheres.