The simple model that of Lindemann

This model makes a simple distinction between molecules without the critical energy, and those with at least the critical energy, i.e. activated or energized molecules. It takes no account of the fact that activated molecules actually do have vibrational levels of differing energies and that the question is it as easy to activate a molecule to the first vibrational level above the critical as it is to activate the molecule to a high vibrational level could be asked. Intuitively this seems unlikely. As shown in the analysis of Problem 4.20 this assumption is unlikely to be correct. 

Again this implies that no distinction is made between differing energy levels above the critical. Energy transfer experiments show that this is a better approximation than the corresponding activation assumption, in so far as one collision is often 

Intuitively, it would seem that a vibrationally very excited molecule is more likely to fly apart than is a molecule with a low vibrational energy. 

As seen in Problem 4.20 it is unlikely that the assumptions given above are all correct. Experiment shows that at least one of k, k, and k2 depends on the vibrational energy. 

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