Potential Energy Surface and Product Branching Ratios for the Reaction of C(3Pj) with the Allyl Radical: An ab Initio/RRKM Study

Ab initio G2M(MP2)//B3LYP/6-311G** calculations have been carried out to investigate the potential energy surface for the C(3Pj) + C3H5(X 2A1) reaction. The results show that C(3Pj) can add without a barrier either to a terminal CH2 group of the allyl radical to form a metastable intermediate INT1 or between two CH2 groups to produce a bicyclic structure INT2. INT1 immediately isomerizes to buta-1,3-dien-4-yl (INT3), which can decompose to vinylacetylene + H or to the vinyl radical + acetylene. Buta-1,3-dien-4-yl (INT3) can also rearrange to 1,2-dien-4-yl (INT4), and the latter fragments by the H atom loss to vinylacetylene or butatriene. The alternative pathway from the reactants to 1,2-dien-4-yl (INT4) involves two sequential ring openings in the bicyclic intermediate INT2. 1,2-dien-4-yl (INT4) can also rearrange to but-2-yn-1-yl (INT7), which in turn decomposes to butatriene + H. The RRKM theory has been applied to compute rate constants for unimolecular reaction steps and the product branching ratios....