Electron scavenging specificity

In applying the quasi-ballistic model to electron scavenging, Mozumder (1995b) makes the plausible assumption that the electron reacts with the scavenger only in the quasi-free state with a specific rate fesf. Denoting the existence... 

The rate of uracil photolysis is affected by the fraction of oxygen content in the solution,7,291 64 and is also affected by dissolved N20.65 The data of Burr and Park are shown in Table III. The effect of N20 upon the rate suggests the intervention of solvated electron intermediates in the reaction mechanism if N20 is, as is commonly supposed, a scavenger specific for electrons. 

As expressed by reaction (VIII), all positron scavengers characterized in polar solvents lead to partial inhibition and therefore are supposed to react specifically with the localized particles. The reasons for this are not well established but, in the same way as for those Solutes that are very poor quasi-ffee electron scavengers although reacting effectively with the solvated electron (e.g., H+), the explanation may lie on thermodynamics. Too much energy may be released upon reaction with the quasi-free particles, either e or e+, so that the bound-state is unstable localization or solvation would reduce the energetics of the process, allowing the reaction to occur. Note that most of the partial inhibitors, whether electron (e.g. H+, Tl+) or positron (Cf,... 

Studies to date on the effects of electron scavengers on the yields of high molecular weight products of solvent decomposition indicate that the effect of a given solute is specific to the solute used (56, 57, 58). 

Shaede and Walker studied the reaction of sodium amalgam with water in the presence of dinitrogen monoxide and methanol at various pH values. Radiolysis experiments had already established that dinitrogen monoxide is a very efficient, specific electron scavenger... 

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... 

Table II. A Comparison of Specific Reaction Rates of Some Electron Scavengers with (Au°)e-a(l and with Other Transient Monovalent Cations"...

Inoue, K., Murayama, S., Seshimo, F., Takeba, K., Yoshimura, Y., and Nakazawa, H. (2005). Identification of phenolic compound in manuka honey as specific superoxide anion radical scavenger using electron spin resonance (ESR) and liquid chromatography with coulometric array detection. /. Sci. Food Agric. 85, 872-878. 

To obtain the attachment reaction efficiency in the quasi-free state, we denote the specific rates of attachment and detachment in the quasi-free state by kf and kf respectively and modify the scavenging equation (10.10a) by adding a term kfn on the right-hand side, where is the existence probability of the electron in the attached state. From the stationary solution, one gets kf/kf = (kfk ikfkf), or in terms of equilibrium constants, K(qf) = Kr.Kr, where k, and k2 are the rates of overall attachment and detachment reactions, respectively. Furthermore, if one considers the attachment reaction as a scavenging process, then one gets (see Eq. 10.11) = k f fe/(ktf + kft) = fe,f/(l + Ku) and consequently k2 = kfKJ(l + KJ. 

The comparatively high ionisation potential of sulphur hexafluoride and its inertness toward attack by thermal hydrogen atoms have lead to its use as a specific scavenger for electrons in several irradiated systems. This has already been illustrated in section 1.7.2. The ionisation processes in SF6 have been studied by beam techniques171, but to date there has been no investigation of its radiolysis per se. Such a study would be well worthwhile. 

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