Electronic coupling metal-dependent effects

The question of metal dependent effects on electronic coupling requires detailed examination. There are two possible sources for such effects ... 

The values of the electron relaxation rates of the coupled metal ion strongly depend both on the relative electron relaxation rates of the isolated ions and on the value of the magnetic coupling constant J. When the absolute value of J (expressed as J /K) is smaller than both electronic relaxation rates, no effect on the electronic relaxation of the pair is expected. When J /H > (electron relaxation rate of the first ion) but smaller than T[ 2) (electron relaxation rate of the second ion), from first order perturbation... 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

When two metals or alloys are joined such that electron transfer can occur between them and they are placed in an electrolyte, the electrochemical system so produced is called a galvanic couple. Coupling causes the corrosion potentials and corrosion current densities to change, frequently significantly, from the values for the two metals in the uncoupled condition. The magnitude of the shift in these values depends on the electrode kinetics parameters, i0 and (3, of the cathodic and anodic reactions and the relative magnitude of the areas of the two metals. The effect also depends on the resistance of the electrochemical cir-... 

Cementation, the deposition of small amounts of an auxiliary metal on a support metal, has been used for a long time as an activation method. A common example is surface alloying with mercury, i.e., amalgamation. The properties of the couple largely depend on the redox potentials of both constituents. In general, the base metal is considered to behave as an electron source, while the "true chemistry" is effected by the superficial auxiliary metal. Several examples illustrate this principle. 

In metal particles, the main consequence of changes in the electron-phonon couplings is a variation of the electron relaxation rates. This effect depends strongly on the intensity regime of the excitation, but experiments carried out at weak excitation on Ag and Au nanoparticles in various matrices show a strong increase of the relaxation rate, i. e. a decrease of the electron-lattice energy exchange time, with quantum confinement (see Fig. 5.3-8) [3.54]. In this case also, the increased... 

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