An ab initio molecular dynamics study of the S_N2 reaction Cl^-+CH₃Br→CH₃Cl+Br^-

An ab initio molecular dynamics study of the S_N2 reaction Cl^-+CH₃Br→CH₃Cl+Br^- has been performed at the Becke, Lee, Yang, and Parr (BLYP) level of theory by the blue-moon method. The potential energy and the free energy profile along the reaction coordinate have been determined and compared with the available experimental and calculated data. An analysis of the structural parameters along the reaction pathway is presented. Results of impact studies are also reported. It is shown that, depending on impact velocity, recrossing of the barrier can occur. Strong polarization effects are reported.