Eree-Electron Energy

Figure 3.6 shows the various relationships between the energy levels of solids and liquids. In electrolytes three energy levels exist, Ep, redox, Eox and Ered- The energy levels of a redox couple in an electrolyte is controlled by the ionization energy of the reduced species Ered, and the electron affinity of the oxidized species Eox in solution in their most probable state of solvation due to varying interaction with the surrounding electrolyte, a considerable... 

Ph ERe(CO) (1,10-phenanthroline) (E = So, Ge) Emission at 298 or 77 K E-Re Bond Dissociation Electronic Energy Transfer Electron Transfer... 

FIGURE 22.2 Electron energy levels for a standard pair of hydrated redox particles and for an intrinsic semiconductor ered = the most probable electron level of oxidant, eox = the most probable electron level of reductant, 8p(redox) = standard Fermi level of redox electrons, 8p = Fermi level of an intrinsic semiconductor, v = valence band edge level, and c = conduction band edge level. 

Figure 6. Energies of a redox system in its oxidized and reduced states. The energy difference Ered ox and Ep.redox are electron energies.

Calculations were done with a full-potential version of the LMTO method with nonoverlapping spheres. The contributions from the interstitial region were accounted for by expanding the products of Hankel functions in a series of atom-ce- -ered Hankels of three different kinetic energies. The corrected tetrahedron method was used for Brillouin zone integration. Electronic exchange and correlation contributions to the total energy were obtained from the local-density functional calculated by Ceperley and Alder " and parametrized by Vosko, Wilk, and Nusair. ... 

At the standard equilibrium potential eox = ered changing the electrode potential by an overpotential r/ lowers the energy of the oxidized state, where the electron has been transferred to the electrode, by —... 

Pig. 2-37. Redox reaction cycle FeJ5 - Fejj + ei iD, - FeJ in aqueous solution solid arrow=adiabatic electron transfer, dotted arrow = hydrate structure reorganization X = reorganization energy ered.d = most probable donor level eox.a = most probable acceptor level. 

Electron-transfer reactions are normally performed in polar solvents such as acetonitrile (MeCN), in which the product ions of the electron transfer are stabilized by the strong solvation [6,7]. When a cationic electron acceptor (A ) is employed in electron-transfer reactions with a neutral electron donor (D), the electron transfer from D to A+ produces a radical cation (D +) and a neutral radical (A ). In such a case, the solvation before and after the electron transfer may be largely canceled out when the free-energy change of electron transfer is expected to be rather independent of the solvent polarity. The solvent independent value is confirmed by determination of the Eqx values of alkylbenzene derivatives (electron donors) and Ered values of acridinium cations (electron acceptors) in solvents with different polarities [79]. The E°ox values of alkylbenzene derivatives in a less polar solvent (CH2CI2) are shifted to the positive direction by about 0.1 V... 

V. D. Parker [56] obtained in acetonitrile the oxidation and reduction potentials (EQx and ERea) of alternant aromatic hydrocarbons (AAH) by cyclic voltammetry and examined how those potentials are related to the ionization potential (IP) and the electron affinity (EA) of the compounds (Table 8.8). As expected, he found linear relations of unit slopes between E0x and IP and between ERed and EA. Moreover, he found that E0x and ERed of each AAH was symmetrical with respect to a common potential MAAH (-0.31 V vs SCE). The values of (E0x-MAAH) and (ERed Maa ) are correlated with the values of IP and EA, obtained in the vacuum, by E0x-Maah = IP- +AGsV+ and ERed-MAAII = liA-r/t-AG, respectively (Fig. 8.21). Here, is the work function of graphite and equal to 4.34 eV, and AGj v+ and AG v are the differences in solvation energies for the 0/+1 and 0/-1 couples of AAH. Experimentally, AG°V+ and AG°V were almost equal, not depending on the species of AAH, and were equal to -1.94 eV in AN. 

Fig. 8.21 Relationship between the oxidation potential (E0x)> the reduction potential (ERed), the ionization potential (IP), the electron affinity (EA), and the solvation energies (AG°V+,...

The loss of an electron by M, M + + e, is the process of oxidation in electrochemistry. The electron is then accepted by an electrode of well defined potential, so that the oxidation potential Eox is the free energy of the reaction, as was seen in Figure 4.1. Similarly the reduction potential Ered is the energy of the reduction reaction, e.g. N + e - N. By definition the molecule, which is oxidized, is the donor (M in this case), and the molecule, which is reduced, is the acceptor. The electron transfer from M to N is therefore equivalent to the combined oxidation of the donor and reduction of the acceptor, so that the energy balance is... 

The band bending eVbb at n-type semiconductors is expected to decrease EB and additional changes of are related to changes of the electron affinity x (fig 1). As the band bending can possible be reserved by illumination a light induced opposite shift of the spectrum equivalent to a photopotential (Uph) is expected. The relation between the electrochemical energy scale Ered/ox vs NHE and the absolute energy scale E vs vacuum level is made by the relation ... 

The fluorescence intensity of ZnP CONH Q is significantly quenched compared to the reference ZnP compound without Q due to efficient ET from the singlet excited state ( ZnP ) to Q in ZnP—CONH—Q (68). Such efficient ET results from the large driving force of electron transfer (—AGej = 0.91 eV in PhCN), which is determined from the one-electron oxidation potential of the ZnP moiety (Eox = 0-78V vs SCE), the one-electron reduction potential of the Q moiety (Ered = —0.36 V vs SCE), and the singlet excited-state energy of ZnP (2.05 eV). 

---