Quantum calculation of the quasi-equilibrium constant involved in the formation of 49O3

At the beginning of the 1980s, measurements in the stratosphere revealed an enrichment of the heavy isotopes 17O and 18O in ozone O3, described as anomalous because it was much higher than statistically expected. In addition, this was roughly equal between 17O and 18O. This effect, called mass-independent fractionation (MIF), remains unexplained despite numerous theoretical and experimental studies. However, it has been shown that the origin of MIF is directly linked to strong isotopic effects found in the recombination reaction O + O2 + M → O3 + M, where M is a third body that absorbs excess energy. Here, we are interested in one of the elementary processes involved in this reaction, namely the rapid quasi-equilibrium process O + O2⇌O3*, where O3* is metastable ozone. A fully quantum approach was used to calculate the quasi-equilibrium constant of this process, giving the most accurate value of this quantity to date for the 49O3 isotopic variant of ozone. The present work represents an important step toward a better understanding of ozone formation and may help contribute to unraveling the mystery of MIF.