Electron scavenger concentration, dependence

The approach based on the LH equation, or the related Eley-Rideal mechanism [30], is common in the literature today [5]. The equation is generally derived assuming equal steady-state concentrations of charge carriers or their concentration independent of substrate and the electron scavengers concentration. The independence of the actual concentration of active species (either h + or ecu) is also usually assumed by taking a mean time of survival of these species independent on other system concentrations. However, it is obvious from the oldest literature that the concentrations of the active species are mutually dependent. The first factor is the recombination in bulk. Bahnemann et al. derived the transient... 

Since, on this view, hydrogen atoms and hydroxyl radicals react to form the products, the sum of the yield of aldehyde (G 1.9) and of 2,3-hutanediol (G 1.6) at pH 1.2 under vacuum should approximate to G(H) + G(OH). The value 3.55 is in reasonable agreement with values from other systems at this pH. It would not appear necessary, therefore, to invoke the concept of sub-excitation electrons. The concentration dependence may be an indication that a solute concentration of 3 or 4 X 10 M is necessary for scavenging all of the hydroxyl radicals and hydrogen atoms available. 

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. 

Balkas Tl, Fendler JH, Schuler RH. (1970) Radiolysis of aqueous solutions of methyl chloride. The concentration dependence for scavenging electrons within Spurs. J Phys Chem 74 4497. 

Quantitative evaluation of the number of radicals shows that, although the nature of the spectrum depends on the concentration of ethyl mercaptan, the total radical yield remains constant this suggests that the protective effect of the additive is due to a competition between electron scavenging by the additive and recombination with cations in the matrix, leading to scission of the polymer chain. The mechanism... 

Concentration Dependence of Electron Scavenging in Single Solute Systems... 

Figure 3. Dependence of the hydrogen yield on concentration of electron scavenger O, CH3Cl A, SF6 , CHsBr A, NgO and , COg. Concentrations of SF6i CHsCl, NgO and C02 have been normalized by factors of a8/acHSBr 0.35, 1.0, and 0.5 respectively) as described in the text. Solid curve is given by Equation VIII...

The concentration dependence for the secondary reactions of negative ions in the above situation will be to a first approximation of the same form as that for electron scavenging—i.e.,... 

Until 1970, pulse radiolysis studies were limited to those species with lifetime >10" sec and observations on the hydrated electron were therefore carried out using only dilute solutions of scavenger. More recently, it has been possible to develop pulses of lO" sec and consequently it has been possible to study much earlier events in the radiolysis and also to study the disappearance of the hydrated electron in concentrated scavenger solutions. Rate coefficients have been found to depend on the concentration of scavenger [66—68]. Thus in the competition of hydrogen ion and acetone for the hydrated electron, viz. 

Before analyzing the different theories concerning the dependence of Gr on pH and electron scavengers, I shall review and analyze different systems, to determine and verify whether there is an actual dependence of Gr on pH and scavenger concentrations. 

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