Practical evaluation of the unimolecular reaction rate

Second, we must know something about the decay rate constants for those of the states which are capable of converting themselves into product. Let us assume that within the rth grain the appropriate decay constants are d,-, with corresponding state degeneracies g, ., whence the required mean decay rate constant for the whole grain will be 

we must know something about the collisional transition rates between the grains, and many models have been explored in the past, particularly those known as the step-ladder and the exponential models [72.R 73.F 77.T1] I will confine myself almost exclusively in this discourse to the strong collision model, equation (2.26), and for the time being, at least, the apparent rate constant p for the relaxation of the total internal energy can be regarded as an adjustable parameter. 

---