An ab initio study on the formation of interstellar tricarbon isomers 1-C3(X1Σg+) and c-C3(X3A′2)

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(P-3(j)) + C2H(X(2)Sigma(+)) and CH (X(2)Pi(Omega)) + C-2(X(1)Sigma(g)(+)) reactions. Both reactions are shown to proceed by barrierless additions of C(P-3(j)) and CH to C2H and C-2, respectively, to produce the c-C3H((XB1)-B-2) and 1-C3H(X(2)Pi(Omega)) intermediates with high exothermicities, which can rearrange to each other via a barrier of 27 kcal/mol. 1-C3H fragments into 1-C-3(X(1)Sigma(g)(+)) + H(S-2(1/2)) (the major product), and c-C3H dissociates to c-C-3 (X(3)A'(2)) + H(S-2(1/2)) (the minor product), both without an exit barrier. The reactions represent facile neutral neutral pathways to produce tricarbon isomers in interstellar environments. (C) 2002 Elsevier Science B.V. All rights reserved.