An ab initio study on the formation of interstellar tricarbon isomers l-C3(X1Σg+) and c-C3(X3A2′)

Ab initio CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311G(d,p) calculations have been performed to investigate potential energy surfaces of the C(3Pj)+C2H(X2Σ+) and CH(X2ΠΩ)+C2(X1Σg+) reactions. Both reactions are shown to proceed by barrierless additions of C(3Pj) and CH to C2H and C2, respectively, to produce the c-C3H(X2B1) and l-C3H(X2ΠΩ) intermediates with high exothermicities, which can rearrange to each other via a barrier of 27 kcal/mol. l-C3H fragments into l-C3(X1Σg+)+H(2S1/2) (the major product), and c-C3H dissociates to c-C3(X3A2′)+H(2S1/2) (the minor product), both without an exit barrier. The reactions represent facile neutral–neutral pathways to produce tricarbon isomers in interstellar environments.