Ozone formation in ternary collisions: Theory and experiment reconciled

TL;DR

This study develops a theoretical model for ozone formation via ternary collisions, computes rate coefficients across a wide temperature range, and aligns well with experimental data, revealing different mechanisms at various temperatures.

Contribution

The paper introduces the first calculation of rate coefficients for ozone formation in ternary collisions as a function of energy and temperature, bridging theory and experiment.

Findings

Ozone formation involves complex mechanisms varying with temperature.

Rate coefficients agree with experimental data from 100-900 K.

Most initially formed O$_3$ molecules are weakly bound.

Abstract

Absorbing UV radiation, ozone protects life on Earth and plays a fundamental role in Earth's temperature balance. The formation of ozone occurs through the ternary recombination reaction: O$_2$+O+M $\rightarrow$ O$_3$+M, where M can be N$_2$, O$_2$ or Ar. Here, we developed a theoretical approach capable of modeling the formation of ozone molecules in ternary collisions, and applied it to the reaction with M=Ar because of extensive experimental data available. The rate coefficients for the direct formation of O$_3$ in ternary collisions O+O$_2$+Ar were computed for the first time as a function of collision energy, and thermally-averaged coefficients were derived for temperatures 5-900~K leading to a good agreement with available experimental data for temperatures 100-900~K. The present study shows that the formation of ozone in ternary collisions O+O$_2$+Ar at temperatures below 200~K proceeds through a formation of a temporary complex ArO$_2$, while at temperatures above 1000~K, the reaction proceeds mainly through a formation of long-lived vibrational resonances of O$_3^*$. At intermediate temperatures 200~K-1000~K, the process cannot be viewed as a two-step mechanism. In addition, it is found that the majority of O$_3$ molecules formed initially are weakly bound.