Ozone Formation in Ternary Collisions: Theory and Experiment Reconciled

Area of Science:

• Atmospheric Chemistry
• Chemical Physics
• Quantum Mechanics

Background:

• Ozone (O3) formation in the stratosphere is primarily driven by ternary collisions involving oxygen atoms (O), oxygen molecules (O2), and a third body (M).
• Understanding the temperature-dependent mechanisms of ozone formation is crucial for atmospheric modeling and predicting stratospheric composition.

Purpose of the Study:

• To investigate the temperature-dependent mechanisms of ozone formation in ternary collisions (O+O2+M).
• To compute rate coefficients for ozone formation without relying on simplified two-step approximations.
• To compare theoretical predictions with experimental data across a wide temperature range.

Main Methods:

• Development of a theoretical approach to model ozone formation in ternary collisions.
• Application of the theory to the O+O2+Ar reaction system.
• Computation of collision energy-dependent rate coefficients.
• Derivation of thermally averaged coefficients from 5-900 K.

Main Results:

• Ozone formation proceeds via temporary complex formation (MO2) below 200 K and long-lived resonances (O3*) above 700 K.
• An intermediate temperature regime (200-700 K) requires a non-two-step mechanism.
• Computed rate coefficients show good agreement with experimental data (100-900 K) when vibrational quenching is considered.

Conclusions:

• The study provides a more accurate, temperature-dependent description of ozone formation mechanisms.
• The findings challenge the universal applicability of simplified two-step models for ozone formation.
• The theoretical framework and computed rate coefficients enhance atmospheric chemistry models.