Strong overlap electron transfer

Strong interaction electron transfer—The electron orbitals of the electrolyte phase reactants directly overlap with those of the electrode phase, with the reactants adsorbed on the electrode surface. 

The specific interaction between the electrode material and some of reacting species has to be defined formally by the overlap of the electronic states of the reactant and the electrode material at the transition state. A weak overlap electron-transfer reaction is defined as that in which the energy of the transition state is not affected by the proximity of the reacting species to the electrode. Conversely, in strong overlap... 

Equations (B5.3.1) and (B5.3.4) also assume that the reacting system is in thermal eqmlibrium with its surroundings. This assumption can be problematic for a reactant that is created by photoexcitation. In addition, Eqs. (B5.3.3) and (B5.3.4) require electronic interactions of the donor and acceptor to be weak. The interaction matrix element//21 for electron transfer depends on the electronic orbital overlap of the reactants, which drops off rapidly as the intermolecular distance increases [101] but can be relatively strong for electron transfer from excited tryptophans to nearby residues and backbone amide groups in proteins [50, 51]. 

Consider the case where the interaction between the molecules A and B is not yet very strong. The magnitude of Hq>P is almost linear with So,p, so that the second-order term in Eq. (3.9) is proportional to the square of So,p. The order of magnitude of So,p is equal to the rth power of an overlap integral s of an MO a of the molecule A and an MO b of the molecule B, where y is the minimum number of electron transfers between A and B required to shift the electron configuration from 0 to p. Therefore, the terms from monotransferred configurations in Eq. (3.9) have magnitudes of the order of Sab, while the monoex. and the ditr. terms are of Sob, and the monoex.-monotr. term s , the diex. term s , and so on. If the interaction is weak and s0 is small, the mono-transferred terms are important in comparison with the others. 

In this model, one considers the acetals to be composed of polarizable dipolar moieties that can be stabilized by electron transfer from an electron-rich moiety (non-bonding electron on oxygen low ionisation energy) to adjacent polar and polarizable moieties (high electron affinity). A strong overlap between n(O) and cr c 0 orbitals optimizes this electronic transfer. As these orbitals are not spherical, n(0)/ct c o overlap depends on... 

Fig. 6. Distribution of Fe2+/Fe3+ reorganization energies found in the MD simulation of electron transfer in a hydrolyzing solution of Fe3+ (the Fe2+ could hydrolyze, but never does) at an apparent pH near 3.9. The strongly overlapping distributions show almost no shift in reorganization energy as a function of hydrolysis, indicating that the hydrolysis fluctuations lie on a continuum with all other solvent fluctuations.

The tunnelling process evidently may have a transmission coefficient smaller than unity, especially when there is insufficient orbital overlap between e q and the acceptor orbital (geometrical hindrance or thickness of barrier). In such cases, the transmission coefficient depends strongly on the gain in free energy on electron transfer AO). When there is a... 

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