KINETICS OF THE GAS-PHASE REACTIONS OF CL- WITH CH3BR AND CD3BR - EXPERIMENTAL-EVIDENCE FOR NONSTATISTICAL BEHAVIOR

The reactions of Cl- with CH3Br and CD3Br have been studied as a function of ion-neutral average center-of-mass kinetic energy, [KE(cm)], at several temperatures. The reactions are inefficient, proceeding at only a few percent of the collision rate. Both increasing temperature and increasing kinetic energy are found to decrease the rate constant as approximately T-0.8 or [KE(cm)]-0.8. The rate constants were found to be independent of pressure at 300 K. At a fixed [KE(cm)], no dependence of the rate constants on temperature was found. This indicates that the rate constants for the reactions do not depend on the internal temperature of the CH3Br or CD3Br. By comparison with other systems, we conclude that rotational excitation of the CH3Br should have little effect on the rate constants. Combining the apparent lack of a rotational dependence and the fact that significant amounts of the CH3Br or CD3Br molecules are vibrationally excited leads to the conclusion that the rate constants are also not strongly dependent on vibrational energy.