Lindemann-Christiansen hypothesis

According to the Lindemann-Christiansen hypothesis, formulated independently by both scientists in 1921, all molecules acquire and lose energy by collisions with surrounding molecules. This is expressed in the simplified form of the Lindemann mechanism, in which we use an asterisk to indicate a highly energetic or activated molecule, which has sufficient energy to cross the barrier towards the product side, and M is a molecule from the surroundings M may be from the same type as A ... 

Figure 5.4 sketches the potential energy curves for dissociation and isomerization in one dimension. In both cases the molecule has to gain sufficient energy to undergo reaction. The Lindemann-Christiansen hypothesis, formulated independently by both scientists around 1921, says the molecule acquires the necessary energy by collisions with other molecules, after which it can either lose its energy in a subsequent collision, or cross the transition barrier to form products. The process is represented schematically by... 

This problem was resolved in 1922 when Lindemann and Christiansen proposed their hypothesis of time lags, and this mechanistic framework has been used in all the more sophisticated unimolecular theories. It is also common to the theoretical framework of bimolecular and termolecular reactions. The crucial argument is that molecules which are activated and have acquired the necessary critical minimum energy do not have to react immediately they receive this energy by collision. There is sufficient time after the final activating collision for the molecule to lose its critical energy by being deactivated in another collision, or to react in a unimolecular step. 

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