DFT study on the mechanism of the CF3OÂ +Â NO reaction

The singlet potential energy surface of the CF3O + NO reaction has been studied at the B3LYP/6-311+G(3df) level of theory. The relative energies were calculated by using the CCSD(T)/aug-cc-pVDZ and the G3B3 methods at the B3LYP/6-311 + G(3df) optimized geometries. The study shows that the reaction starts via an exothermic barrierless addition of NO to the CF3O radical to produce cis-CF3ONO, which will isomerize to trans-CF3ONO, followed by trans-CF3ONO dissociating to the products CF2O + FNO. trans-CF3ONO can also rearrange to trans-CF3OON and further isomerize to cis-CF3OON. Once cis-CF3OON is formed, it will finally dissociate to CF2O + FNO. This is another energetically facile reaction route to produce CF2O + FNO. The transition states involved in above reaction pathways all lie below the reactants in energy, thus the present calculations suggest the overall rate coefficient of the title reaction may exhibit a negative temperature dependence, in agreement with most experimental results. Additionally, the enthalpies of formation of CF3NO2, trans-CF3ONO and cis-CF3ONO were computed to be ΔfH298.15∘(CF3NO2) = −160.99 kcal/mol, ΔfH298.15∘(trans-CF3ONO) = −176.76 kcal/mol and ΔfH298.15∘(cis-CF3ONO) = −173.24 kcal/mol, respectively.