Adiabatic and Nonadiabatic Transfer

The interaction matrix element, H12, is chosen to fit the actual energy difference between the PES when Rj = Rj. This energy difference can be calculated in a quantum chemical calculation where Q = 0. If the calculated energy difference is A, we choose H,2= A/2. With this substitution and the one of Equation 10.25 the new PES are obtained from Equation 10.21  

FIGURE 10.6 PES for a symmetric ET system. X is the reorganization energy A the avoided crossing gap at Q = 0. 

The avoidedness, that is, the value of A, clearly depends on how closely the two metal complexes are located to each other, whether they have any ligand in conunon, etc. If we assume that the distance between the two complexes tends to infinity, the energy difference A at the avoided crossing clearly tends to zero and we have two parabolic energy surfaces without interaction, called diabatic PES. 

At the normal distance, there is always some interaction (A 0). If A is so small that the final PES cannot be easily distinguished from the diabatic ones, we are talking about nonadiabatic ET. If, on the other hand, A is so large that the lower PES may be regarded as an ordinary ground state of the system at aU Q - Qo, we are talking about adiabatic ET. 

If kQo IHjjI, there is only one minimum, for Q = 0. Each minimum corresponds to an equilibrium point for the total system. 

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