Franck-Condon restrictions

The electron-transfer process must take place without violating the Franck-Condon restriction, namely, that none of the atoms involved change position during the instant (< 10-14 sec) of the actual electron transfer. As it is rather unlikely that the acceptor molecule should have an electron vacancy at its vibrational and electronic ground state, most eJTq reactions must result in the formation of excited molecules as their primary products. It is probable that after accommodating an additional electron the interatomic bond distances, and in many cases the whole... 

The incorporation of the Franck-Condon restriction leads to the partitioning of an electron-transfer reaction into reactant (precursor complex) and product (successor complex) configurations. The steps in Equations (6.13) to (6.15) go from reactants to products K is the equilibrium constant for the formation of the precursor complex [Aqx, Bred], and is the forward electron-transfer rate to produce the successor complex [Area, Box]-... 

If the Franck-Condon restriction applies to reactions producing e aq, then, for those processes discussed later which require the solvation energy of e aq to be available, either the electron binding of e aq must be principally by electronic rather than electron-dipole interaction or the electron is rapidly caught in a pre-existing polarized site in the solvent. In any event, there is not time for electron-induced orientational polarization. The measured mobility and diffusion constant of e aq is also consistent with this view because during the relaxation time of the water... 

The ability of a metal to act as an electron donor or acceptor is very dependent upon the type and arrangement of the ligands surrounding the metal. This is true thermodynamically and kinetically. The electron density at the metal is ligand-de-pendent as is the overall stability of the complex. The ease of electron-transfer process itself is dependent not only upon the reduction potential but also the geometry of the complex because of Franck-Condon restrictions. 

The electron transfer can only take place when the M-L bond distances in the M(II) and M(in) states are the same, i.e. the bonds in [ML ] " must be compressed and those in [MLg] must be elongated (Figure 26.10). This is described as a Franck-Condon restriction. The activation energy... 

The electron transfer can only take place when the M-L IxHid distances in the M(II) and M(III) states are the same, i.e. the bonds in [MLe] must be compressed and those in [MLs] must be elongated (Fig. 26.10). This is described as a Franck-Condon restriction. The activation energy required to reach these vibrational excited states varies according to the system, and hence the self-exchange rate constants vary. In the case of [Fe(bpy)3] and [Fe(bpy)3] ", both complexes are low-spin, and the Fe-N bond distances are 197 and 196 pm, respectively. Electron transfer involves only a change from ia/ to hg (Fe " and vice versa. 

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