Theoretical Studies of the Reaction Dynamics of the Matrix-Isolated F2+cis-d2-ethylene System

摘要

The molecular dynamics of the F, + cis-d, -ethylene addition reaction and thesubsequent decomposition dynamics of the vibrationally excited 1,2-difluoroethane-d, product isolated in Ar or Xe matrices at 12 K are investigated using trajectory methods that incorporate nonstatistical sampling to enhance the reaction probabilities. The matrix is represented by a face-centered-cubic crystal containing 125 unit cells with 666 lattice atoms in a cubic (5 X 5 X 5) arrangement. Both interstitial and substitutional sites for the F21cis-d2 -ethylene pair are examined. Transport effects of the bulk are simulated using the velocity reset method introduced by Riley, Coltrin, and Diestler J. Chem. Phys. 88, 5934 (1988). The potential-energy hypersurface for the system is written as the separable sum of a lattice potential, a lattice-substrate interaction, and a gas-phase potential for 1,2-difluoroethane-d2. The first two of these have pairwise form, while the 1,2-difluoroethane-d, potential is identical to that employed previously to study the unimolecular reaction dynamics of matrix-isolated 1,2difluoroethane-d, J. Chem. Phys. 93, 3160 (1990). The major F, + cis-d2-ethylene reaction mechanism involves a four-center, concerted aB3 addition across the C = C double bond. A small contribution from an atomic addition mechanism that initially forms fluoroethyl and fluorine radicals is observed in a xenon matrix, but not in argon.