Solvent Dynamical Effects in Electron Transfer: Predicted Influences of Electron Coupling upon the Rate-Dielectric Friction Dependence

The predicted dependence of the bimolecular rate constant for outer- sphere electron exchange, k sub ex, upon the longitudinal relaxation time, tau sub L, for Debye solvents is examined numerically on the basis of a suitably combined rate formulation in order to examine the manner and extent to whic...

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Bibliographic Details
Main Authors: Gochev, A, McManis, G E, Weaver, M J
Format: Report
Language:English
Subjects:
ADIABATIC CONDITIONS
BARRIERS
COEFFICIENTS
COMPUTATIONS
COUPLING(INTERACTION)
CROSSINGS
DYNAMICS
ELECTRON ACCEPTORS
ELECTRON DONORS
ELECTRON TRANSFER
ELECTRONS
FORMULATIONS
INTERACTIONS
MOLECULES
NUMERICAL ANALYSIS
Physical Chemistry
RATES
REACTANTS(CHEMISTRY)
RELAXATION TIME
SEPARATORS
SOLVATION
SOLVENTS
SPATIAL DISTRIBUTION
TRANSMITTANCE
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Summary:The predicted dependence of the bimolecular rate constant for outer- sphere electron exchange, k sub ex, upon the longitudinal relaxation time, tau sub L, for Debye solvents is examined numerically on the basis of a suitably combined rate formulation in order to examine the manner and extent to which the rate-solvent friction dependence, of particular experimental significance, should be sensitive to the degree of donor-acceptor electronic coupling and related factors. The treatment accounts for the contributions to k sub ex from a spatial distribution of reactant pairs as well as for the effects of donor- acceptor interactions upon the unimolecular rate constant, k sub et (1/s), for each encounter geometry. The latter include the influence of electronic interactions as prescribed by the matrix coupling element, H12, upon the effective frequency for adiabatic barrier crossings, nu sub n, as well as upon the electronic transmission coefficient, K sub el (i.e. the degree of reaction nonadiabaticity). The anticipated dependence of the free-energy barrier, as well as nu sub n and K sub el, upon the donor-acceptor separation is accounted for in the k sub ex calculations. Numerical comparisons are made with corresponding log k sub ex - log(1/tau sub L) plots obtained using the simple encounter preequilibrium treatment which presumes that only a fixed narrow range of encounter-pair geometries contribute to k sub ex. While the form of plots are not greatly smaller slopes. Some corresponding numerical calculations for electrochemical-exchange reactions are also included.