Plane of electron transfer

For the evaluation of the non-faradaic component of the response in a more realistic way, different proposals have been made. A useful idea is that corresponding to the interfacial potential distribution proposed in [59] which assumes that the redox center of the molecules can be considered as being distributed homogeneously in a plane, referred to as the plane of electron transfer (PET), located at a finite distance d from the electrode surface. The diffuse capacitance of the solution is modeled by the Gouy-Chapman theory and the dielectric permittivity of the adsorbed layer is considered as constant. Under these conditions, the CV current corresponding to reversible electron transfer reactions can be written as... 

The plane of electron transfer is, in reality, a zone given that the transfer can occur some distance away from the outer Helmholtz plane (OHP) via tunnelling [1]. 

Suppose that due to insufficient supporting electrolyte being present, an uncompensated potential difference A< ex exists between the plane of electron transfer (PET) and the outer edge of the double layer. Suppose additionally that within the double layer, the concentration of the electroactive species A is equilibrated, and hence obeys the Boltzmarm equation ... 

Fig. 7.19 A diagram showing the change in potential as a function of the distance from the electrode. The molecules of the redox species are situated on the plane of electron transfer.

So long as the solution is well supported, an alteration to E produces an equivalent alteration to (0m - 0s,bulk)- If there is a significant potential difference between the plane of electron transfer and bulk solution, however, then ... 

In fluoran 50, the methyl group at 3 -position causes steric hindrance to the adjacent anilino group resulting in torsion of the anilino group from the xanthene plane. Consequently, electron transfer from the anilino group to the xanthene moiety is hindered more or less, resulting in hypsochromic shift of the absorption at 610 nm to 570 nm (violet in color). On the other... 

The reaction of electron transfer at electrodes in aqueous electrolytes proceeds either with hydrated redox particles at the plane of closest approach of hydrated ions to the electrode interface (OHP, the outer Helmholtz plane) or with dehydrated and adsorbed redox particles at the plane of contact adsorption on the electrode interface (IHP, the inner Helmholtz plane) as shown in Fig. 7-2. 

Figure 16 (a) Location of the x2 - y2 (planes) and z2 - y2 (chains) bands in the 1-2-3 superconductor showing plane-chain electron transfer and the removal of the half-filled x2 - y2 band, (b) Variation in Tc with oxygen atom stoichiometry showing the dramatic plunge at around S = 0.6. (c) Location of the x2 - y2 (planes) and z2 - y2 (chains) bands in the 1-2-3 system for S > 0.6 showing how plane-chain electron transfer is switched off and the half-filled x2 -y2 band is generated. 

Photoinduced Electron Transfer. Monolayer organizates are particularly suited for the investigation of photoinduced electron transfer, since the molecules are fixed and the distance between the planes at which the donor and the acceptor molecules, respectively, are located can be well defined. Therefore, complex monolayers have been arranged in order to study the distance dependence of electron transfer in these systems (2, 20). This strategy has also been used to elucidate the relative contributions of electron injection and energy transfer mechanisms in the spectral sensitization of silver bromide (21). 

Despite the presence of four bridging groups the quinone is not held rigidly above the plane of the porphyrin. Two channels of electron transfer from the singlet excited state of the porphyrin were found for this compound [145]. They were ascribed to slowly equilibrating introverted and extroverted conformers in which the estimated interplanar porphyrin.quinone separation is respectively, 6.5 and 8.5 A. The faster of the two rate constants is independent of the temperature over the range 80-300 K. 

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