Hyperthermal O-Atom Exchange Reaction O2 + CO2 through a CO4 Intermediate

O2 and CO2 do not react under ordinary conditions because of the thermodynamic stability of CO2 and the large activation energy required for multiple double-bond cleavage. We present evidence for a gas-phase O-atom exchange reaction between neutral O2 and CO2 at elevated collision energies (∼160 kcal mol−1) from crossed-molecular-beam experiments. CCSD(T)/aug-cc-pVTZ calculations demonstrate that isotope exchange can occur on the ground triplet potential energy surface through a short-lived CO4 intermediate that isomerizes via a symmetric CO4 transition state containing a bridging oxygen atom. We propose a plausible adiabatic mechanism for this reaction supported by additional spin-density calculations.