Ab initio direct dynamics trajectory study of the Cl-+CH(3)ClS(N)2 reaction at high reagent translational energy

An ab initio (HF/3-21+G*) direct dynamics quasiclassical trajectory study w as performed for the Cl- + CH3Cl S(N)2 reaction at a reagent relative trans lational energy of 100 kcal/mol. Initial conditions for the trajectories we re averaged over the orientation of CH3Cl and the reaction dynamics studied versus collision impact parameter. The trajectories reacted by a backside attack mechanism and reaction by frontside attack was not observed. The cal culated backside reaction cross reaction is 0.22-0.40 Angstrom(2) and appro ximately two to four times larger than the experimental value (J. Phys. Che m. A 1997, 101, 5969). The absence of reaction by frontside attack was inve stigated by initiating trajectories at the C-s transition state for the fro ntside attack mechanism. These trajectories formed Cl- + CH3Cl reactants wi th a large vibrational energy and low relative translational energy, which suggests extensive CH3Cl vibrational excitation is needed to access the fro ntside reaction pathway.