Electron scavenging theory

For cyclohexane solutions the yield of nitrogen exceeds that caused by electron scavenging (as given by theory or by the 2,2,4-trimethylpentane results). This excess yield can be reasonably accounted for if nitrous oxide reacts with some cyclohexane derived intermediate which... 

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. 

Hayon endeavored to prove that Ge is equal to 2.3 at low concentrations of electron scavenger, where keaq+s[S] < 107, and at higher concentrations follows G(e ) = 2.3 + f(ke +s[S]). The function (/(fc6 q+s[S] ) is given as an experimental curve (47), Hayon believes that the observed spread in Ge is caused only by the different values of fceaq+s[S] in the systems which were studied and proposes a theory (45). However, on checking his data, it can be shown that in these systems, an appreciable—if not the entire—effect of the decrease in Geaq as the concentration of S decreases, is caused by eaq competition with the irradiation products formed. 

The observed G values satisfactorily fix a general curve with only one parameter, kR+s [scavenger] (47). My criticism of the theory is identical with that of the diffusion model. I do not expect a general behavior of eaq scavengers on the yield. The product of the reaction of the different scavengers with the electrons yield products which are not identical and thus have different reactivities with other radicals in the spur. Furthermore, it was demonstrated earlier that in many cases the observed yields at low scavenger concentrations are incorrect since initial yields were not always measured. 

There are two important differences between photoemission into vacuum and into condensed media. Firstly, the work function in the latter case usually (but not necessarily) is lowered because of an interaction of the photoelectron with the solvent. Further, chemical reactions are possible with deliberately introduced scavengers or trace impurities present in an electrolyte. Secondly, the presence of an electrical double layer introduces a potential drop across the Helmholtz plane and diffuse layer. In some earlier theories, the electrical double layer in the presence of solute molecules was thought to screen effectively the positive charge remaining after the electron is emitted (unlike the case of emission into vacuum), thereby reducing image effects and changing the theoretical form of the photocurrent rate expressions. 

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