Isotope Photochemistry

Oxygen and carbon isotope fractionation associated with products (CO and O2) of gas phase photodissociation of CO2 have been studied using photons from Hg lamp (184.9 nm) and Kr lamp (123.6 nm and 116.5 nm). In dissociation by Hg lamp photons both CO and O2 are enriched in 17O by about 81 ¿ compared to the estimate based on a kinetic model. Additionally, CO is enriched in 13C by about 37 ¿ relative to the model composition. In contrast, in dissociation by higher energy Kr lamp photons no such anomaly was found in O2. 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 17O and 13C. The 17O enrichment is higher than that of 13C by a factor of 2.2±0.2 which can be explained by the known magnetic moment ratio of 17O and 13C due to differing nuclear spins and g-factors. These results have potential implications in studies of the planetary atmospheres.