Determination of intramolecular isotope distribution of ozone by oxidation reaction with silver metal
Résumé
The intramolecular distribution of 17O in ozone was determined by a new technique using oxidation reaction of ozone with silver and measuring the isotope ratios 18O/16O and 17O/16O of silver oxide, ozone and leftover oxygen. These data along with known 18O distribution in ozone given by Janssen (2005) in terms of r50 = [16O16O18O]/[16O18O16O] allow us to determine r49 = [16O16O17O]/[16O17O16O]. It is seen that r49 values increase from 2.030 to 2.145 with increase of bulk 17O enrichment in ozone from 11.7‰ to 106.3‰ (controlled by varying temperature and pressure during ozone formation) just as r50 values increase from 1.922 to 2.089 with increase in bulk 18O enrichment over the same range. Over bulk enrichment level up to ∼100‰ the r49 values are higher than r50 values by 0.075 ± 0.026. The difference is small but significant since it corresponds to a large change in enrichment values of the asymmetric and symmetric types of 17O16O2 and 18O16O2 relative to a hypothetical ozone standard with statistical isotope distribution. The difference reduces with increase in bulk ozone enrichment. We do not find any significant variation in r values between ozone samples made by Tesla discharge and by UV photolysis of oxygen. Additionally, for ozone samples with negligible enrichment, the symmetrical isotopomers have relatively more heavy isotopes than the asymmetrical ones consistent with their bond strength difference. Atmospheric implications of the results are briefly discussed.
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