Electron scavenger solvation

Emission of electrons from the electrode into the solution with formation of solvated electrons and the subsequent reaction between the solvated electrons and the electron scavenger in solution. 

Encounter radii for reactions of the solvated and hydrated electrons with various electron scavengers, corrected for electrolyte screening... 

Effective encounter distances for reaction of solvated electrons with electron scavengers at room temperature compared with crystallographic encounter distances Unless otherwise noted, the solvent is water (containing an inert electrolyte in some cases). Corrections for ionic interactions according to eqn. (106) were applied and reaction rate coefficient were extrapolated to zero ionic strength (Chap. 3, Sect. 1.6 and 1.7). Many of these studies have been mentioned in Chap. 3, Sect. 2... 

Effective encounter distances for reactions of solvated electrons with electron scavengers at low temperatures, compared with crystallographic encounter distances, from a fit between experiment and eqn. (105)... 

A characteristic reaction of CTTS excited states is photoelectron production with concomitant oxidation of the metal center.107 In the example given in equation (46),108 electrostatic repulsion of the primary photoproducts facilitates their separation and allows direct observation of the solvated electron. In other systems, photoelectron production has been inferred from the products observed in the presence of an electron scavenger such as N20 or CHC13.109... 

Cathodic currents are stimulated by the illumination of metal electrodes [55-59]. These currents are often strongly enhanced by the presence in solution of known electron scavengers such as N20 and H30+. Research carried out by Barker [59— 61], Pleskov [62-64], Delahay [65], and their co-workers indicates rather strongly that the impinging photons eject electrons from the electrode surface. They appear to travel some distance ( 50 A) before becoming solvated [55,59,62,65]. If a scavenger is present, the solvated (usually aquated) electrons may react with it irreversibly. For example,... 

Absorption Spectrum of e aq. The absorption spectrum of the hydrated electron is shown in Figure 1. The evidence that this spectrum is that of eaq is at least four-fold. First, the spectrum is suppressed by known electron scavengers, such as H30+, 02, N20 (4, 18). Second, it resembles in form the absorption bands of the solvated electron in liquid ammonia and methylamine (4, 18). Third, the rate constants calculated from the decay of this absorption in the presence of scavengers... 

Aliphatic Compounds. Saturated hydrocarbons as well as alcohols, amines and ethers are unreactive toward e"aq, as are also their fluoro derivatives (43, 69, 10). This is not surprising since the elements of the first series when bound by a bonds have no vacant orbital to accommodate an additional electron. Hydrocarbons cannot solvate electrons because of their low polarity, but alcohols and amines can be used in pure form as solvating media for electrons (12, 43, 45). If our hypothesis on the role of solvation of OH in the e aq + H20 reaction is correct, it is expected that, if alcohols are purified to eliminate the last traces of electron scavengers, eioiv will survive in them much longer than in water, owing to the lower stability of alkoxy ions in alcohols. The same should be true of alkyl amines and diamines. 

In case of electron scavenging (and no Ps lifetime quenching, as is true for both Cl" and Tl+), no other positron states are present than free e+ and Ps then, the intensities from PALS and from DB are the same. The p-Ps and o-Ps intensities are expected to decrease so that the fwhm of the DB spectra should increase with solute concentration (the narrow components are suppressed). The variations of fwhm with C can be completely calculated, knowing the intensities Ij from PALS and the Tj previously established for a given solvent. This is illustrated by the solid line in Figure 4 for Tl+ this ion, as expected from its high solvated electron scavenging rate constant, is thus shown to suppress Ps formation by electron capture. 

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,... 

Figure 1 shows tJie corresponding optical absorption spectra of these radical cations as taken in the pulse radiolysis of the pure solvents. To avoid the influence of solvated electrons, in the case of alkanes, an electron scavenger such as tetrachloromethane is usually added [see Eq. (5b)]. Alkyl chlorides are internal electron scavengers and do not need further additives. In most of the cases, for the study of electron transfer reactions of type 2 or 3, the solvent derived radicals do not disturb because of their much lower reactivity compared with those of the ions. 

The reaction with halocarbons results in loss of halide, with concurrent Ibrmation of halocarbon-derived free radicals, R (eq 5) (47). Zepp and co-vorkers (12) used the photoproduction of chloride ions from the halocarbon, 2-chloroethanol, a known solvated electron scavenger, in solutions of NOM... 

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