Ozone Formation in Ternary Collisions: Theory and Experiment Reconciled

The present Letter shows that the formation of ozone in ternary collisions O + O2 + M—the primary mechanism of ozone formation in the stratosphere—at temperatures below 200 K (for M=Ar) proceeds through a formation of a temporary complex MO2, while at temperatures above ∼700 K, the reaction proceeds mainly through a formation of long-lived vibrational resonances of O*3. At intermediate temperatures 200–700 K, the process cannot be viewed as a two-step mechanism, often used to simplify and approximate collisions of three atoms or molecules. The developed theoretical approach is applied to the reaction O + O2 + Ar because of extensive experimental data available. The rate coefficients for the formation of O3 in ternary collisions O + O2 + Ar without using two-step approximations were computed for the first time as a function of collision energy. Thermally averaged coefficients were derived for temperatures 5–900 K. It is found that the majority of O3 molecules formed initially are weakly bound. Accounting for the process of vibrational quenching of the nascent population, a good agreement with available experimental data for temperatures 100–900 K is obtained