Theoretical Study on Mechanism of C5H7·+O2 Reaction

The potential energy surface (PES) for the reaction of E,E-pentadienyl with molecular oxygen was theoretically studied at the G3B3//B3LYP/6-311G(d,p) level of theory. The first step of the reaction was found to be the direct adduction of molecular O2 on either the C1 or the C3 atoms of E,E-pentadienyl, forming two C5H7O2· isomers. These two C5H7O2· isomers undergo a series of isomerization processes through either the hydrogen-transfer or cyclization pathway. In the final step, the hydrogen-transferred and cyclized isomers decompose into unsaturated aldehydes, unsaturated ketones, and hydroxyl radicals. Involves 20 stable species and 14 transition states, and the energies and structures of all reactants, products and transition states were calculated. Based on the calculated barriers and heats of formation, the authors suggest that the C2H3O·+C3H4O formation channel is the dominant channel for the C5H7·+O2 reaction. The possible existence of C5H7O2· radicals as long lifetime intermediates is also proposed, which is consistent with the recent photoionization mass spectrometric experiments by Zils et al.