Ozone Formation in Ternary Collisions: Theory and Experiment Reconciled

The present Letter shows that the formation of ozone in ternary collisions O + O-2 + 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 similar to 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 + O-2 + Ar because of extensive experimental data available. The rate coefficients for the forniation of O-3 in ternary collisions O + O-2 + 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 O-3 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.

Automated summary

This letter investigates the ozone formation mechanism in ternary collisions O + O-2 + M at different temperatures through theoretical modeling and experimental data. It is found that at low temperatures, ozone is formed through the formation of a temporary complex MO2, while at high temperatures, it mainly occurs through the formation of long-lived vibrational resonances of O-3*. At intermediate temperatures, the process cannot be simplified as a two-step reaction mechanism.