Global analytical representations of the three lowest potential energy surfaces of C2H, and rate constant calculations for the C(P-3)+CH((2)Pi) reaction

Potential energy surfaces for the first three electronic states of the reac tion C(P-3) + CH(X (2)Pi) --> C-2 + H have been constructed from a new set of high level ab initio data which are of the multireference configuration interaction variety and were carried out using a polarised triple-zeta basi s set. These are the X (2)Sigma(+) and the A (2)Pi states, and lead to the formation of C-2(X (1)Sigma(g)(+)) and C-2(a (3)Pi(u)) considering an adiab atic dissociation process. Each adiabatic potential is expressed within the double many-body expansion (DMBE) scheme which is based, in this case, on the extended Hartree-Fock approximate correlation energy model (EHFACE). Mo reover, a quasiclassical trajectory study of the title reaction has been pe rformed for each of the three potential energy surfaces, yielding the corre sponding rate constants.