CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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energy barrier. Therefore it is clearly apparent that electron transfer involves both change in
solvent configuration and chemical structure. It is clear from the above description if we
assume that electron transfer takes place from equilibrium configurations we will end up with
a different vibrational configuration after electron transfer event. Therefore, such a reaction
happening in dark leads to non-conservation of energy. To get away from this conundrum
Marcus hypothesized that before electron transfer happens, energies of ions are matched.
Additionally energy conservation and validity of Franck-Condon principle is strictly
maintained in case of weak interaction between the ions.
1. 6. 1. Adiabatic and Non-Adiabatic Process
Fig 1. 12 gives potential energy surface of reactant and products R and P respectively.
The interaction between reactant and product is assumed to be weak therefore splitting is
assumed to be < kT. Reactant and product PES is labeled R and P respectively. If the
electronic interaction is very weak the splitting at the intersection of the two surfaces is
negligible. In the first case the system will always remain on the lowest surface as it moves
from left to right such a process is called an adiabatic electron transfer this happens in the
case where splitting is large. In the other case as reaction proceeds, the reactant remains in
the same potential energy surface. Such a transfer is called non adiabatic process [1. 44].