Kinetic origin of the ozone isotope effect: a critical analysis of enrichments and rate coefficients

The oxygen isotope anomaly in ozone was first identified in isotopomers 49O3 and 50O3 with enrichments of over 10%. Recent rate coefficient measurements imply a new interpretation of the anomaly. The large variability of the rate coefficients of ozone formation O + O2 → O3 of about 50% characterizes the ozone isotope effect and demonstrates its kinetic origin. Surprisingly, the rate coefficients correlate with the zero-point energy change of the oxygen molecules participating in the isotope exchange reactions but not with the mass of the ozone molecules. Rate coefficients of symmetric molecules depart from this linear relationship by about 20%.