Abstract
Ab initio calculations at the EOM-CCSD and CASSCF-CASPT2 level have been carried out for low lying triplet states of C2H2. Minima on the seam of crossing and dissociation transition states have been found. At a photon energy slightly above the H + C2H(X (2) Sigma) asymptote, we propose the following pathway for photodissociation from the S-1 state; C2H2 first hops to T- 3 upon symmetric H-C-C bending and torsion, then adiabatically travels onto T-2 along asymmetric H-C-C bending and finally hops to T-1 to dissociate to H + C2H(X (2) Sigma). The proposed mechanism and the reverse barrier height on T-1 are consistent with recent experimental observations. (C) 1997 Elsevier Science B.V.
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