Determination of intramolecular isotope distribution of ozone by oxidation reaction with silver metal

Abstract

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.