RRKM calculations inertia

The procedure adopted here is to make use again of RRKM theory to calculate k2/k l as a function of the relative barrier height. In this case, the transition state for the, reaction is taken as the loose ion-molecule complex at the Langevin capture distance. The transition state for the reaction k2 is taken as the tetrahedral intermediate RCOYX ". By a suitable choice of the vibrational frequencies and moments of inertia, this type of calculation shows that E 0-E0 for Cl- + CH3COCl should be around — 7 kcal mol 1 in order to reproduce the experimental efficiency. This amounts to an E 0 of 4 kcal mol-1. 

An example of the limiting RRKM k E) curve is shown in figure 7.4 for the bromobenzene ion dissociation. In this case, only three vibrational frequencies are lost, two going to rotations and one to translation. The two lowest frequencies were replaced by two rotors with moments of inertia equal to 80 amu-A. Although the rates are about a factor of 10 too high, the slope is much closer to that of the calculation with the five lowest frequencies reduced to 115 cm". ... 

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