Diffusion kinetic analysis of spur-decay processes

4 DIFFUSION KINETIC ANALYSIS OF SPUR-DECAY PROCESSES 

Samuel and Magee [436] suggested that the reaction probability between two such radicals both formed at r0, t0 is the volume integral of the product of the density of one radical times that of the other 

When there are N radicals present, there are (N/2) (N — 1) ways of choosing pairs of radicals and so the rate of reaction of radicals becomes [437] 

If the initial distribution of radicals is Gaussian with variance a2 about r0, the density of any one of the radicals is 

Schwarz [438] has extended the analysis to include all of the species thought to be important in the radiation chemistry of water, namely e j, H+, OH , H20, H2, 02 (Sect. 4.2). He has found that the coulomb 

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 

2—20 reactive species. Homogeneous reactions do not occur until after 1 ps i.e. when the locally high concentration of reactants in spurs has decayed by reaction and the residual non-uniform concentrations near spur sites have been diminished further by diffusion of the reactants 

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