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

The kinetics of electronically inelastic quenching of O2(a1Δg) and O2(b1Σg+) 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(b1Σg+) and O2(a1Δg) 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.