Specific vibration of the activated complex along the reaction coordinate leads to product formation. We need to express K of eq. (33.11) in terms of molecular characteristics. In the present case, they are the molecular partition functions. In Lecture 29, we have already learnt that the population of electronic, vibrational, rotational and translational levels is governed by their energies and the temperature through molecular partition functions.
Consider the energy levels for the following equilibrium,
A
B
(33.12)
The energy levels of systems containing only A, only B and both A and B are schematically shown in fig (33.2)
Figure 33.2 (a) Energy levels of individual molecules A, B and the individual populations of these levels, (b) Energy levels of the combined system A and B and the relative populations of the combined levels at equilibrium (schematic).
B 
