Kinetics of electrons

Madey T E ef a/1993 Structure and kinetics of electron beam damage in a chemisorbed monolayer PFjOn Ru(OOOI) Desorption Induced by Electronic Transitions DIET V vol 31, ed A R Burns, E B Stechel and D R Jennison (Berlin Springer)... 

Influence of the Kinetics of Electron Transfer on the Faradaic Current The rate of mass transport is one factor influencing the current in a voltammetric experiment. The ease with which electrons are transferred between the electrode and the reactants and products in solution also affects the current. When electron transfer kinetics are fast, the redox reaction is at equilibrium, and the concentrations of reactants and products at the electrode are those specified by the Nernst equation. Such systems are considered electrochemically reversible. In other systems, when electron transfer kinetics are sufficiently slow, the concentration of reactants and products at the electrode surface, and thus the current, differ from that predicted by the Nernst equation. In this case the system is electrochemically irreversible. 

Heterogeneous electron reactions at liquid liquid interfaces occur in many chemical and biological systems. The interfaces between two immiscible solutions in water-nitrobenzene and water 1,2-dichloroethane are broadly used for modeling studies of kinetics of electron transfer between redox couples present in both media. The basic scheme of such a reaction is... 

Kinetics of Electron-Ion Recombination in Irradiated Dielectric Liquids... 

KINETICS OF ELECTRON-ION RECOMBINATION IN IRRADIATED DIELECTRIC LIQUIDS3... 

The kinetics of electron-ion recombination is well described by the diffusion model both for photoionization and for ionization induced by high-energy irradiation. 

A question arises as to what happens if the Nernstian approximation breaks down. Under these circumstances, we must use the proper equations for the kinetics of electron transfer discussed in chapter 1. The simplest case is that of a completely irreversible system, where only oxidation (or reduction) is possible and a single electron is transferred, i.e. consider the process ... 

Nelly R.N., Schulman S.G., Proton-Transfer Kinetics of Electronically Excited Acids and Bases, in Molecular Luminescence Spectroscopy Methods and Applications, part 2, Schulman S.G. (ed.), Wiley-Interscience, New York, 1988 pp 461-510. 

Jin, Q. and C. M. Bethke, 2002, Kinetics of electron transfer through the respiratory chain. Biophysical Journal 83, 1797-1808. 

The structure of HRP-I has been identified as an Fe(IV) porphyrin -ir-cation radical by a variety of spectroscopic methods (71-74). The oxidized forms of HRP present differences in their visible absorption spectra (75-77). These distinct spectral characteristics of HRP have made this a very useful redox protein for studying one-electron transfers in alkaloid reactions. An example is illustrated in Fig. 2 where the one-electron oxidation of vindoline is followed by observing the oxidation of native HRP (curve A) with equimolar H202 to HRP-compound I (curve B). Addition of vindoline to the reaction mixture yields the absorption spectrum of HRP-compound II (curve C) (78). This methodology can yield useful information on the stoichiometry and kinetics of electron transfer from an alkaloid substrate to HRP. Several excellent reviews on the properties, mechanism, and oxidation states of peroxidases have been published (79-81). 

If the kinetics of electron transfer does not obey the Butler-Volmer law, as when it follows a quadratic or quasi-quadratic law of the MHL type, convolution (Sections 1.3.2 and 1.4.3) offers the most convenient treatment of the kinetic data. A potential-dependent apparent rate constant, kap(E), may indeed be obtained derived from a dimensioned version of equation (2.10) ... 

As with the other reaction schemes involving the coupling of electron transfer with a follow-up homogeneous reaction, the kinetics of electron transfer may interfere in the rate control of the overall process, similar to what was described earlier for the EC mechanism. Under these conditions a convenient way of obtaining the rate constant for the follow-up reaction with no interference from the electron transfer kinetics is to use double potential chronoamperometry in place of cyclic voltammetry. The variations of normalized anodic-to-cathodic current ratio with the dimensionless rate parameter are summarized in Figure 2.15 for all four electrodimerization mechanisms. 

The information thus obtained on the redox properties of the radicals is a global reduction potential in which the thermodynamic and kinetic parameters are intermingled [equation (2.39)]. It is possible to separate these parameters if it is assumed that the kinetics of electron transfer to the radical obeys the MHL law in its approximate quadratic version (see Section 1.4.2) ... 

Effect of surface chelation on the kinetics of electron transfer from the conduction band of Ti02 to methylviologen (MV2+). Oscillograms showing the time-dependent growth of the MV+ absorption at 630 nm after laser excitation (at 355 nm) of aqueous solutions (pH 4.85) containing colloidal Ti02 (1 g/e) and 10 3 M MV2+ ... 

Macroscopic n-type materials in contact with metals normally develop a Schottky barrier (depletion layer) at the junction of the two materials, which reduces the kinetics of electron injection from semiconductor conduction band to the metal. However, when nanoparticles are significantly smaller than the depletion layer, there is no significant barrier layer within the semiconductor nanoparticle to obstruct electron transfer [62]. An accumulation layer may in fact be created, with a consequent increase in the electron transfer from the nanoparticle to the metal island [63], It is not clear if and what type of electronic barrier exists between semiconductor nanoparticles and metal islands, as well as the role played by the properties of the metal. A direct correlation between the work function of the metal and the photocatalytic activity for the generation of NH3 from azide ions has been made for metallized Ti02 systems [64]. 

In order to probe these effects, a number of studies on the kinetics of electron transfer between small molecule redox reagents and proteins, as well as protein-protein electron transfer reactions, have been carried out (38-41). The studies on reactions of small molecules with electron transfer proteins have pointed to some specificity in the electron transfer process as a function of the nature of the ligands around the small molecule redox reagents, especially the hydrophobicity of these... 

We consider a simple redox electron transfer of hydrated redox particles (an outer-sphere electron transfer) of Eqn. -1 at semiconductor electrodes. The kinetics of electron transfer reactions is the same in principal at both metal and semiconductor electrodes but the rate of electron transfer at semiconductor electrodes differs considerably from that at metal electrodes because the electron occupation in the electron energy bands differs distinctly with metals and semiconductors. 

As discussed in Sec. 8.3.5, a redox reaction current due to electron or hole transfer depends not only on the concentration of interfadal electrons or holes at the electrode but also on the state density of the redox electrons or redox holes in the range of energy where the electron transfer takes place. Hence, it is important in the kinetics of electron or hole transfer to realize the level of the band edge Cc or Ev of the electrode relative to the most probable level cred or cox of redox electrons or redox holes in the hydrated redox particles. 

In Chapter 7 general kinetics of electrode reactions is presented with kinetic parameters such as stoichiometric number, reaction order, and activation energy. In most cases the affinity of reactions is distributed in multiple steps rather than in a single particular rate step. Chapter 8 discusses the kinetics of electron transfer reactions across the electrode interfaces. Electron transfer proceeds through a quantum mechanical tunneling from an occupied electron level to a vacant electron level. Complexation and adsorption of redox particles influence the rate of electron transfer by shifting the electron level of redox particles. Chapter 9 discusses the kinetics of ion transfer reactions which are based upon activation processes of Boltzmann particles. 

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