Effects of reaction path curvature on reaction dynamics and rates: Reaction path Hamiltonian calculations for gas-phase SN2 reaction Cl−+CH3Cl

✍ Scribed by Yoshishige Okuno

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 239 KB
• Volume: 68
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1998)68:4<261::aid-qua4>3.0.co;2-t

✦ Synopsis

To obtain essential information on the reaction dynamics for the prototype gas-phase S 2 reaction Cl y q CH Cl ª ClCH q Cl y , the characteristic N 3 3 features of the potential energy surface in the local region around the reaction path were examined by the reaction path Hamiltonian constructed with high-level ab initio molecular-orbital calculations. After the structures of relevant stationary states and the intrinsic reaction coordinate were determined, the transverse vibrational modes, the corresponding frequencies, and the coupling elements between the pairs of normal modes induced by the reaction coordinate motion were calculated at each point along the intrinsic reaction coordinate. It was found that a quite large reaction path curvature appears in the intrinsic barrier slope near the bottom of each of the pre-and postreaction stable-state complexes. This large curvature was clarified to cause the internal vibrational excitation of the products and the requirement of the vibrational excitation of the reactants for reaction occurrence. The complex recrossings across the transition-state w theory dividing surface, previously characterized by Hase et al. J. Chem. Phys. 96, 8275 Ž .x y 1992 in which trajectories trapped in the Cl иииCH Cl complex return to the central 3 barrier region, were demonstrated to be attributed to this large curvature. Furthermore, not only the variational effects but also the reaction path curvature effects on the intermediate recrossings that were also characterized by Hase et al., in which trajectories linger near the central barrier, were found to be negligible.