Electron scavenging kinetics

Burns and Curtiss (1972) and Burns et al. (1984) have used the Facsimile program developed at AERE, Harwell to obtain a numerical solution of simultaneous partial differential equations of diffusion kinetics (see Eq. 7.1). In this procedure, the changes in the number of reactant species in concentric shells (spherical or cylindrical) by diffusion and reaction are calculated by a march of steps method. A very similar procedure has been adopted by Pimblott and La Verne (1990 La Verne and Pimblott, 1991). Later, Pimblott et al. (1996) analyzed carefully the relationship between the electron scavenging yield and the time dependence of eh yield through the Laplace transform, an idea first suggested by Balkas et al. (1970). These authors corrected for the artifactual effects of the experiments on eh decay and took into account the more recent data of Chernovitz and Jonah (1988). Their analysis raises the yield of eh at 100 ps to 4.8, in conformity with the value of Sumiyoshi et al. (1985). They also conclude that the time dependence of the eh yield and the yield of electron scavenging conform to each other through Laplace transform, but that neither is predicted correctly by the diffusion-kinetic model of water radiolysis. 

To evaluate the absolute kinetics of recombination from Eq. (7.27), it is necessary to obtain a reliable value of fes in addition to a measured from scavenging experiments. For electron scavenging in cyclohexane by biphenyl, Rzad et al. (1970) used fes = 3.0 x 10u M s-1 on the basis of the a value of scavenging... 

A study of electron scavenging in multipair clusters [21] has shown that the total scavenging probability decreases with increasing number of ion pairs in the cluster. However, the Laplace transform relationship [Eq. (28)] between the scavenging probability and the recombination kinetics was found to work reasonably well also in the multipair case. 

Transient radicals and radical cations generated by the 7- and photo-irradiative oxidation of thioxanthene in the presence of an electron scavenger have been characterized spectroscopically and kinetically (Scheme 57) <1996JPC13539>. 

However, Stern Volmer kinetics are obeyed for radiolysis studies of scavenging of toluene fluorescence with benzyl chloride. The electron scavengers CHCl and chlorobenzene reduce the fluorescence yields of arenes in a manner that suggests ... 

However, photocatalytic reduction of organic compounds is generally less important than their oxidation because the reduction potential of a Ti02(e ) is lower than the oxidation potential of a Ti02(h ). Also, most of the reducible substrates cannot compete kinetically with oxygen as an electron scavenger [15]. 

Kinetics of Positive-Charge and Electron Scavenging and the Kinetics of Charge Neutralization in the Radiolysis of Dielectric Liquids. J. Chem. Phys. 46, 2822 (1967). 

When an electron scavenger is present, electrons may be captured before recombination. Electron capture must initially result in the formation of a molecular anion with internal energy equal to the sum of the electron affinity of XY and the kinetic energy of the incident electron. 

Kinetics of Electron Scavenging. If a single characteristic lifetime, t = l/ku could be ascribed to the geminate recombination process... 

Kinetic studies of the competitive reactions of other electron scavengers support this hypothesis (18, 20). In the radiolysis of solutions of nitrous oxide in alkanes, reactions with other intermediates must be considered. Radicals, hydrogen atoms, and positive ions can be eliminated (5, 20), but a reaction with excited molecules is possible. It has been reported... 

Specific electron scavengers suppress the transient absorption obtained in the pulse radiolysis of water. By measurement of the efficiency of this process, it is possible to determine the rate coefficient for the reaction of the hydrated electron with the scavenger. Solutes are restricted to those which do not absorb significantly in some region of the hydrated electron spectrum. Computer programs have been developed for kinetic analysis of the oscilloscope traces and it is thus possible to obtain rate coefficients... 

Measurement of the effect of electron scavengers on the RH yield show that scavengers are more effective in reducing this yield than they are in scavenging electrons. A kinetic mechanism was proposed in which a fraction of the solvent holes are initially in an excited state that does not yield the solvent Si state upon recombination [53]. The relaxation and fragmentation of the pre-... 

The diffusion kinetic analysis of spur-decay processes requires a model of the initial distribution of reactive species produced by radiolysis. These reactants are able to diffuse from their original location and, if they encounter another reactant, reaction can occur. Most work on spur-decay processes has been with water as the solvent and with such solute species as N2O, HCOO as electron scavenging solutes, OH as a proton scavenger, and alcohols to scavenge hydroxyl radicals. Water is so polar that coulomb interactions may be disregarded and the reactants treated as uncharged radical species. Most of the reactions thought to be important were listed in Sect. 4.2. Many of these reactions occur at or close to the diffusion-limited rate and most of the rate coefficients have been measured. It should be recalled that a spur is a localised cluster of... 

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