Hyperthermal O-atom exchange reaction O2 + CO2 through a CO4 intermediate.

Area of Science:

• Chemical kinetics
• Physical chemistry
• Theoretical chemistry

Background:

• Oxygen (O2) and carbon dioxide (CO2) are generally considered unreactive under ambient conditions due to CO2's thermodynamic stability and high activation energy barriers.
• Understanding reactions between stable molecules is crucial for various chemical processes.

Purpose of the Study:

• To investigate the possibility of a gas-phase O-atom exchange reaction between O2 and CO2.
• To elucidate the reaction mechanism and intermediate species involved.

Main Methods:

• Crossed-molecular-beam experiments were conducted at elevated collision energies (approx. 160 kcal mol(-1)).
• High-level ab initio calculations, specifically CCSD(T)/aug-cc-pVTZ, were employed to model the potential energy surface.
• Spin-density calculations were used to support the proposed reaction mechanism.

Main Results:

• Evidence for a gas-phase O-atom exchange reaction between O2 and CO2 was observed.
• Isotope exchange occurs on the ground triplet potential energy surface.
• A short-lived CO4 intermediate and a symmetric CO4 transition state with a bridging oxygen atom were identified.

Conclusions:

• The study demonstrates that O2 and CO2 can react via O-atom exchange under specific high-energy conditions.
• A plausible adiabatic reaction mechanism involving a CO4 intermediate has been proposed.
• These findings expand the known reactivity landscape of seemingly inert molecules.