Analysis of the reaction paths to dissociation of dichloro-ethylenes into Cl2 and C2H2

The reaction paths to dissociation of dichloro-ethylenes (DCE) into Cl-2 and acetylene (C2H2) in the gas phase were studied, at the CCSD(T)/6-311G(d,p)//CASSCF(6,6)/6-31G(d) level of theory, including zero point energy correction. The structures and energies of reactants, transition states and products were determined through ab initio calculations. There are two principal paths to dissociation. One of them involves a number of transition states and intermediates where internal rotations, H and Cl migrations are involved until the dissociation into Cl and C2H2Cl radicals. The activation energy to this path is about 97 kcal/mol. On the other hand, C2H2Cl radicals were also predicted to be formed directly from cis- and trans-DCE. In addition, we have determined several paths to isomerization among the trans-, cis- and 1,1-dichloro-ethylene. We have concluded that these isomerization paths have activation energies below to the dissociation reaction. Therefore, the dissociation process can proceed from every dichloro-ethylene. (C) 1998 Elsevier Science B.V. All rights reserved.