Reaction cross sections and thermal rate constant for Cl− + CH 3 Br → ClCH 3+ Br− from J-dependent quantum scattering calculations

Abstract

Employing dimensionality-reduced time-independent quantum scattering theory and summation over all possible total angular momentum states, initial-state selected reaction cross sections for the exothermic gas-phase bimolecular nucleophilic substitution (SN2) reaction Cl + CH3Br - ClCH3 + Br have been calculated. The carbon–halogen bonds and the rotation of the methyl halides are taken into account. In agreement with previous calculations for J = 0, initial rotational motion of CH3Br decreases the reaction probability and consequently the cross sections. The experimentally obtained thermal rate constant for 300 K is reproduced within the experimental error. For lower temperatures, it is calculated to be below the experimental values but shows the same strong increase for T - 0.