Can. J. Chem. 54, 275 (1976). It is shown that e,,,,, He, and OH formed by the radiolysis of water by 3 MeV electrons are trapped by nitroso and nitrone compounds to give nitroxides with well defined esr spectra. Three spin trapping agents were used, nitroso-t-butane, phenyl-t-butyl nitrone, and 5,s'-dimethyl pyrroline-I-oxide. The latter was shown to be an excellent con~pound for these studies. Complications due to the instability of some of the nitroxides were overcome by coupling the electron accelerator to the esr spectron~eter to permit direct observation of the spectra. On a montrC que les e,,,,,, Ha, et OH formts par radiolyse de I'eau par des Clectrons B 3 MeV sont captCs par des composes nitroso et nitrone et conduisent B des nitroxydes avec des spectres rpe bien dtfinis. On a utilise trois agents de piCgeage; L e nitroso t-butane, la phtnyl t-butyl nitrone et la dimethyl-5,5' pyrroline oxyde-I. On a n~o n t r i que ce dernier composC est excellent pour ces ttudes. On a CliminC les con~plications dues a I'instabilitC de q~~elques nitroxydes en couplant directement I'acctICrateur d'Clectron au spectromktre de rpe pour permettre une observation directe du spectre.[Traduit par le journal]

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Extensive studies of the photobleaching kinetics of e; in aqueous alkaline glasses show (i) that electrons are trapped in potential wells of differing depths from which they can be selectively photobleached, and (ii) that trapping occurs within the Coulombic field of the positive charge produced concurrently with the electron. Examination of other aqueous glasses indicates that the trapped electron is located in a " water-walled " cavity.Electrons detached either photochemically or radiation chemically from molecules in neutral or alkaline aqueous glasses at low temperatures may, after deceleration, be trapped in the matrix in a form designated e;. At 77 K, e; is immobile, has a characteristic singlet e.s.r. spectrum and has an intense visible absorption band with Amax in the range 535-590 nm.I* Several models have been put forward to describe e; in aqueous glasses. Jortner and Scharf proposed that the electron was located in an expanded S orbital of the alkali metal cation, and Moorthy and Weiss that it was bound in an expanded 3s orbital on 0-, the anionic form assumed by the hydroxyl radical in alkaline glass. However, convincing arguments against these proposals are (i) that Schulte-Frohlinde and Eiben have shown that the optical spectrum of e; is unaffected by changing the cation, (ii) when e; is formed in 7 M NaClO, glass a virtually identical spectrum is observed,6 and (iii) that similar spectra displaced to shorter wavelengths are manifested by e; in glassy alcohols which initially contain no anions or cation^.^ Others * have suggested that e; is located in anion vacancies but Bennett, Mile and Thomas have shown that the same optical and e.s.r. spectra are produced when alkali metals and water react in the rotating cryostat when neither 0-nor anions are present. Arguing from the trapping of electrons in alcoholic glasses, Eiben and Schulte-Frohlinde l o have suggested that the electrons are held in pre-existing structural cavities in the medium, and Barzynski and Schulte-Frohlinde have demonstrated conclusively that G (e;) is much smaller in a polycrystalline alcoholic or alkaline aqueous matrix than in an amorphous one.Ershov and Pikaev regard e; as a " peculiar I;-centre ", i.e., the electron is immobilized in a cavity in the medium not far from the positive '' holes " formed during radiolysis. However, the identity of e; produced in alkaline aqueous glass by radiolysis and by photolysis of ferrocyanide ion,12 as well as some of the evidence cited above, does not support this conclusion.

The oxidation and reduction of nitrosobenzene, phenylhydroxylamine, and some of their derivatives have been studied by electron spin resonance methods in a variety of solvents. From the observed spectra the species PhNOand PhfiHO have been identified. PhNOis observed only in strongly alkaline solution and in the immediate vicinity of the cathode during the electrolytic reduction of nitrosobenzene. In neutral or acid solution PhNOis replaced by P h i H O which is identical with the first oxidation product of phenylhydroxylamine. The role of these paramagnetic species in the reduction of aromatic nitro-compounds is discussed briefly.