Isotopic study of the mechanism of ozone formation

The mechanism of ozone formation has been studied using 16 O and 18 O 2 . High‐resolution microwave spectroscopy was used to measure the amounts of the isotopomeric ozone species formed. The study is hampered by the very rapid exchange process between the reactants, that tends to scramble the isotopes and hence give a 2:1 statistical ratio between the two possible isotopomers. We have found a strategy to come around this difficulty and conclude that the mechanism is a simple end‐on‐addition.