Toward Quantitative Reaction Dynamics of O ₃

The reaction dynamics of O( 3 P) + O 2 ( 3 Σ g – ) collisions in the O 3 (X 1 A ′) electronic ground state is characterized on a high-level MRCI+Q/aug-cc-pVQZ potential energy surface (PES) represented as a reproducing kernel. For the atom exchange reactions involving the 16 O and 18 O isotopes with rates k 6 exch ( T ) and k 8 exch ( T ), a negative temperature dependence of k exch ( T ), consistent with experiments was found. The absolute rates typically underestimate measured rates by ∼50%. For the ratio R ( T ) = k 8 exch ( T )/ k 6 exch ( T ), the measured T dependence was correctly captured with a maximum at ∼300 K. The differences between experiments and computations are primarily due to neglect of zero-point effects. For the dissociation reaction, the rate is lower by approximately 1 order of magnitude compared with experiments, which is a clear improvement over simulations using previous PESs. The present results support an electronic degeneracy factor of g e diss ∈ [1/27, 1] with a preference for values toward the lower end of the interval. Nonadiabatic effects are deemed to play only a minor role in the atom-exchange reaction.