Electronic coupling, between donor and

Electronic absorption spectroscopy charge transfer transitions, 19 71 d-d transitions, 19 70, 71 flavocytochrome b, 36 269-271 intraligand transitions, 19 71-80 of organometallics, 19 69-80 Electronic coupling, between donor and acceptor wave functions, 41 278 Electronic nuclear double resonance spectroscopy, molybdenum center probes, 40 13... 

When donor-acceptor pairs lack interactions with an intervening medium, e.g. solvent molecules, the electron transfer mechanism is supposed to occur through space. Considering that the electron density of molecular orbitals falls off exponentially, a similar postulate may be formulated for the electronic coupling between donor and acceptor, fljfg... 

Figure 2.1(a) above illustrates the potential energy surface for a diabatic electron transfer process. In a diabatic (or non-adiabatic) reaction, the electronic coupling between donor and acceptor is weak and, consequently, the probability of crossover between the product and reactant surfaces will be small, i.e. for diabatic electron transfer /cei, the electronic transmission factor, is transition state appears as a sharp cusp and the system must cross over the transition state onto a new potential energy surface in order for electron transfer to occur. Longdistance electron transfers tend to be diabatic because of the reduced coupling between donor and acceptor components this is discussed in more detail below in Section 2.2.2. 

The truly metallic intervalence complexes often suffer from low extinction coefficients despite the low energy gap of the transition, the extent of the electronic coupling between donor and acceptor over the framework chosen remains comparatively small. 

The value of p reflects the efficacy of the medium in coupling the donor and the acceptor. Since electronic coupling between donors and acceptors is often treated in terms of a superexchange model, the decay of electronic coupling is sometimes reported per bond rather than per unit distance. In the bond-coupling model, the exponent in Eq. 5 becomes [- P (A - l)/2]. 

Traditional transition state theory does not hold for longdistance electron transfer reactions. Due to weak electronic coupling between donor and acceptor moieties, formation of a transition state does not necessarily lead to... 

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