Electronically Nonadiabatic Quenching of Excited States of O₂ by Collisions with O Atoms

The kinetics of electronically inelastic quenching of O₂(a¹Δ) and O₂(b¹Σ⁺) by collisions with O(³P) have been investigated using mixed quantum-classical trajectories governed by adiabatic potential energy surfaces and state couplings generated from a recently developed diabatic potential energy matrix (DPEM) for the 14 lowest-energy ³A' states of O₃. Using the coherent switching with decay of mixing (CSDM) method, dynamics calculations were performed both with 14 coupled electronic states and with 8 coupled electronical states, and similar results were obtained. The calculated thermal quenching rate coefficients are generally small, but they increase with temperature. The positive temperature dependence is attributed to high-energy locally avoided crossings that can only be easily accessed by high collision energies. We find that, depending on the temperature, 86-97% of the b state quenches are into the a state with the remainder into the ground electronic state of O₂. The calculated rate coefficients for quenching of O₂(b¹Σ⁺) and O₂(a¹Δ) by O(³P), coupled with the assumption that electronically nonadiabatic probabilities for collisions on the ³A' surfaces are similar to those on ³A″ surfaces, are compared with the available experimental results.