KINETIC-ENERGY AND TEMPERATURE DEPENDENCES FOR THE REACTIONS OF F- WITH HALOGENATED METHANES - EXPERIMENT AND THEORY

Rate constants have been measured as a function of average kinetic energy at several temperatures for the reactions of F- with CH3Cl, CH3Br, and CH3I. The rate constants at low energy approach but are not equal to the collision limiting value. The rate constants for all three reactions decrease slowly with increasing average kinetic energy for energies below 0.2 to 0.3 eV. At 0.2 to 0.3 eV, a break occurs in the slopes of the energy dependence curves. Above these energies the rate constants decrease more rapidly with increasing energy. Trajectory calculations that include a probability function which is dependent upon collision angle were performed in order to examine the effects of orientation on the reactions. The calculations were fitted to the low energy portion of the experimental data. A more severe orientation requirement is found for the lighter halides. The energies at which the breaks occur in the experimental curves are reproduced by the calculations. These energies correspond to the energies at which the hard sphere collision diameter of the colliding partners is equal to the capture radius. © 1990 American Chemical Society.