Ring Formation Mechanism of C4H3 Radical and Acetylene in Soot Precursor Formation

• • DFT/TST calculations reveal that n-C4H3 + C2H2 yields fulvenyl (five-membered ring) as the dominant product, with formation rates ordered fulvenyl > phenyl > four-membered ring, indicating a kinetic preference for five-membered ring closure under combustion conditions. • • For i-C4H3, addition at the C2 position exclusively produces fulvenyl, while addition at C4 yields a mixture of four-, five-, and six-membered rings, with the four-membered ring forming most rapidly and the six-membered ring slowest, highlighting positional control over ring size selectivity. • • The computed barrier heights and rate constants (not explicitly given in the abstract) provide quantitative inputs for chemical kinetic models of soot precursor formation, enabling more accurate predictions of PAH growth in flames. • • The study establishes that isomer-specific reactivity of C4H3 radicals with acetylene is a critical factor in determining the distribution of cyclic intermediates, which directly influences the initial steps of soot nucleation.