AN AB-INITIO INVESTIGATION OF SPIN-ALLOWED AND SPIN-FORBIDDEN PATHWAYS OF THE GAS-PHASE REACTIONS OF O(P-3)+C2H5I

The singlet and tripler potential energy surfaces involved in the gas phase reactive collisions of O(P-3) and C2H5I have been studied with a b initio electronic structure computations. The collisions produce bot h spin-forbidden HOI+C2H4 and spin-allowed OI+C2H5 products. The calcu lations indicate that HOI is formed via a triplet complex and through a tripler/singlet intersystem crossing, followed by passage through a singlet intermediate and transition state for the intramolecular abstr action of beta-hydrogen. All the relevant structures for this pathway are lower in energy than the reactants, and this pathway is accessible even at low impact energies. The calculations also indicate that OI m ay be formed by two channels. One is the same to the above singlet pat hway up to the singlet intermediate, which now dissociates endothermic ally without barrier to give the products. The second channel is the d irect dissociation of the triplet intermediate, and is open only when an enough excess energy to surmount a triplet transition state is prov ided. The product energy distribution is also discussed based on the s tructures of transition states. (C) 1998 American Institute of Physics .