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 O-4 9(3) and O-50(3) with enrichments of over 10%. Recent rate coefficient meas urements imply a new interpretation of the anomaly. The large variability o f the rate coefficients of ozone formation O + O-2 --> O-3 of about 50% cha racterizes the ozone isotope effect and demonstrates its kinetic origin. Su rprisingly, the rate coefficients correlate with the zero-point energy chan ge of the oxygen molecules participating in the isotope exchange reactions but not with the mass of the ozone molecules. Rate coefficients of symmetri c molecules depart from this linear relationship by about 20%.