In Fig 35.3, the time dependence of several pairs of distances in the reaction NaBr + KCl
NaCl +KBr is shown. The transition state is fairly long lived (for 4 ps from 1.5 ps (pico seconds) to 5.5 ps). In this transition region, the distances between all the pairs NaBr, BrCl and KBr are around 500 pm during this period. We can thus conclude that the activated complex is tetraatomic. The complex undergoes nearly 15 oscillations before decomposing into the products. The collision is not a direct one wherein the products are formed "instantly" as in the H2 + H (Fig. 35.2) case.
Figure 35.3 A trajectory for the NaBr + KCl
NaCl + KBr reaction showing the long lived (NaBr...KCl) tetraatomic activated complex.
Example 35.1
Indicate reactive trajectories on an attractive and repulsive PES.
Solution : The trajectories are sketched in Fig. 35.4
Figure 35.4 Reactive (R) and nonreactive (NR) trajectories on an attractive and a repulsive PES.
NaCl +KBr is shown. The transition state is fairly long lived (for 4 ps from 1.5 ps (pico seconds) to 5.5 ps). In this transition region, the distances between all the pairs NaBr, BrCl and KBr are around 500 pm during this period. We can thus conclude that the activated complex is tetraatomic. The complex undergoes nearly 15 oscillations before decomposing into the products. The collision is not a direct one wherein the products are formed "instantly" as in the H2 + H (Fig. 35.2) case. 
NaCl + KBr reaction showing the long lived (NaBr...KCl) tetraatomic activated complex. 
