Inverted free-energy region

The second observation is that photochemically induced electron or hole transfer involves high energies and driving forces. Charge transfer patterns that extend into the inverted free energy region, AG°j have indeed been observed. These are accommodated by the following extension of eq.(6-l)... 

The rate constant drops with increasing aG° in the inverted free energy region, in contrast to the rate constant increase in the normal region, aG° high-frequency nuclear modes is that the rate constant falls off more slowly with increasing aG° as excited vibrational states of the high-frequency mode(s) open new decay... 

Tests of the inverted region for bimolecular electron transfer have proven to be more elusive. As mentioned above, a major difficulty is that, for many bimolecular reactions, vetKA > kD and a large portion of the free energy region of experimental interest is lost because the rate constants... 

Electron transfer corresponds to the transition from U, to at the transitional confignration P. AF is the free-energy of the transition. The lower free-energy snrface of the final state corresponds to the inverted region. 

FIGURE 34.5 Scheme explaining the absence of the inverted region in the electrochemical processes. The position of the free-energy surfaces 7 and U corresponds to the inverted region. However, the major contribution to the current is due to the transition from to U(, which are in activationless configuration. 

Figure 4. Schematic diagram to show the reorganization energy X for nonisotopic reactions for harmonic free energy profiles. This figure shows a normal region activation barrier when-AG° < an activationless situation when -AC =. l.and an inverted region activation barrier when-AG° > A for the harmonic potential inii andGfin represent the initial (reactant) and the final (product) system free energy, respectively.

Another, and even more striking aspect of the variation of the symmetry factor with the driving force is the prediction, from (9) and (10), that an inverted region should exist at large driving forces, i.e. when the inequality (40) applies. The activation free energy is then predicted to increase with the... 

Fig. 18 Free energy surfaces illustrating the activation energy AG for charge recombination in the Marcus inverted region and the coupling term //,y between the initial state, i, and the final state, y...

The free energy for ground-state product formation is correspondingly so negative that this pathway lies in the Marcus inverted region. Consequently both, energetically... 

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