Surprising rate coefficients for four isotopic variants of O+O2+M

Abstract

Mass spectrometric analysis of nonequilibrium oxygen isotopic mixtures undergoing UV photolysis has been employed to study three-body recombination rate coefficients for the O+O2, Q+O2, O+Q2, and Q+Q2 (O=16O, Q=18O) reactions, all with M=80% N2:10% O2:10% Q2 at 200 Torr and 296 K. kO+O2 is in good agreement with the currently recommended value, while kQ+Q2 is only slightly smaller. Surprisingly, kQ+O2 is close to kO+O2, while kO+Q2 is ≈50% larger. As a consequence of this unusual behavior, kO+OQ must be ≈20% larger than kQ+OQ to produce the well-known enrichments that occur in the free atmosphere and in laboratory experiments involving scrambled mixtures. Contrary to what is usually assumed in discussions of the heavy ozone anomaly, these results indicate that isotopic asymmetry does not guarantee a rate coefficient advantage.