The Adiabaticity and Nonadiabaticity in Electron Transfer Reactions

These two possibilities of reaction processes make much difference in calculating the rate of any chemical reaction. According to the transition state theory formalism, these two types of reactions (i.e., adiabatic and nonadiabatic) influence the value of the transmission coefficient, k, which is a preexponential term in the absolute rate expression. The value of k is considered unity for the adiabatic reaction and less than unity for a nonadiabatic reaction. 

Physically, in the adiabatic case, the reactants attract strongly at their closest approach when the probability of reaction is a maximum and the 

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