An explanation for symmetry-induced isotopic fractionation in ozone

Application of a theory of nuclear symmetry-based reaction restrictions to the O₂ + O → O₃ reaction provides a potential explanation for the symmetry-induced isotopic enrichment observed for laboratory and atmospherically produced O₃. Within this theory, the rate of formation of O₃ from collisions of O and isotopically homonuclear O₂ depends on whether the O₂ molecule is in an f (allowed) or an e (restricted) parity label state. The restriction can be relaxed by various potential energy surface coupling terms, and the assumption that approximately 78 percent of the restricted O₂(e) levels produce O₃ with the same efficiency as the allowed O₂(f) levels can account for laboratory-observed isotopic fractionation. In particular, the theory explains the special enhanced formation of the completely asymmetric isotopomer ¹⁶O¹⁷O¹⁸O.