Electron exchange kinetics using

Mechanistic Studies of Electron Exchange Kinetics Using Ab Initio Electronic Structure Techniques... 

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. ... 

Fig. 2-10. Profile of electron density and electronic potential energy across a metal/vacuum interface calculated by using the jellium model of metals MS = jellium surface of metals Xf = Fermi wave length p. - average positive charge density P- s negative charge density V = electron exchange and correlation energy V, - kinetic energy of electrons. [From Lange-Kohn, 1970.]...

The description of bonding at transition metal surfaces presented here has been based on a combination of detailed experiments and quantitative theoretical treatments. Adsorption of simple molecules on transition metal surfaces has been extremely well characterized experimentally both in terms of geometrical structure, vibrational properties, electronic structure, kinetics, and thermo-chemistry [1-3]. The wealth of high-quality experimental data forms a unique basis for the testing of theoretical methods, and it has become clear that density functional theory calculations, using a semi-local description of exchange and correlation effects, can provide a semi-quantitative description of surface adsorption phenomena [4-6]. Given that the DFT calculations describe reality semi-quantitatively, we can use them as a basis for the analysis of catalytic processes at surfaces. 

The significance of these equal and opposite current densities is easy to comprehend. They represent the kinetic side of equilibrium. Equilibrium is not a static business, as it often seems to be from thermodynamics. It is better to regard it as a two-way traffic of ions and electrons across the interface. The word exchange is used quite aptly here—there is an exchange of ions between electrode and solution, and at the equilibrium potential the rate of exchange in each direction is equal in magnitude though opposite in direction. 

Electron transfer may also dominate the excited state chemistry of open shell radical ions. The fluorescence of the radical anions of anthraquinone and 9,10-dicyanoanthracene and the radical cation of thianthrene are quenched by electron acceptors and donors, respectively, although detailed kinetic analysis of the electron exchange do not correspond exactly either with Weller or Marcus theory (258). The use of excited radical cations as effective electron acceptors represents a... 

Ab initio SCF and Mbller Flesset calculations with flexible valence basis sets including 4f orbitals are carried out for the ground and first excited spin states of the Co(NH3)52 and Co(NH3)5 complexes. The results of the calculations in conjunction with a first-order spin-orbit coupling model yield an estimate of 10" for the electronic transmission factor in the Co(NH3)5 exchange reaction using an apex-to-apex approach of reactants, thus providing a mechanism characterized by only a modest degree of non-adiabaticity, consistent with the experimental kinetic data. 

When visual indicators are used, the rate of attainment of equilibrium depends on the type of reaction leading to color development, which may be slow. For simple electron exchange reactions like that of ferroin, the rate of indicator response is usually rapid. If, however, the indicator undergoes a more deep-seated structural change, one can anticipate kinetic complications. The oxidation of diphenylamine, for example, is induced (Section lS-8) by the iron(II)-dichromate reaction. 

ESR experiments were used to measure the kinetics of several types of reactions, those that can be monitored only by ESR, such as proton exchange or electron exchange reactions of radicals, and some that can be measured by other techniques as well, e.g. decay kinetics. Although most decay kinetics of phenoxyl radicals were followed by pulse radiolysis or flash photolysis by monitoring optical absorption, kinetics for some long-lived radicals were frequently monitored by ESR. For example, the second-order decay rates of 4-alkyl-2,6-di-f-butylphenoxyl radicals were measured to be 2200, 500 and 2 s ... 

Furthermore, the diffusion coefficients for triplet exciton migration extracted from this three-dimensional intramolecular model were nearly the same as those obtained using the conventional kinetic equation (i.e. eq 1). The hopping frequencies for triplet exciton migration in PVCA for these three models are summarized in Table 111(20). Neither the electron exchange mechanism(21) nor the Forster... 

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