Theoretical investigation of the decarboxylation reaction of CH₃CO₂ radical

A theoretical study on the decarboxylation reaction of CH₃CO₂ radical at the MP2 level of theory has been carried out. It is found that the thermal reaction CH₃CO₂ → CH₃ + CO₂ may occur on the ²A′(A′) potential energy surface of CH₃CO₂ via a reaction barrier of 4.2 kcal/mol at the PMP4/6-311+G(3df,3pd)//MP2/6-311+G(2df,2p) level of theory. Another possible reaction path is the CH₃CO₂(A′) transform into the CH₃CO₂(A₁) and thus undergo a barrier-less dissociation into the products CH₃ + CO₂. The thermal rate constants of channel CH₃CO₂(A′) → CH₃ + CO₂.were evaluated based on the electronic structure and energy information from the PMP4/6-311+G(3df,3pd)//MP2/6-311+G(2df,2p) level of theory with microcanonical variational transition state theory (μVT) in the temperature range of 200-3000 K. The fitted Arrhenius expression from the forward μVT rate constants within the calculated temperature range is K^{μ VT} = 2.196 × 10¹¹ T^0.294 e^{(- 2.304 × 103 / T)} s^{- 1}. It is also found that the geometry of the CH₃CO₂ radical is sensitive to the basis set used.