The radiolytic yields, a t liquid nitrogen temperature, of trapped electrons and radicals or radical-ions in 2-methyltetrahydrofuran and the yields of these species plus the biphenyl anion in solutions containing biphenyl have been determined by e.s.r. These measurements were also carried out after photolysis of the trapped electrons. The combined results are interpreted in terms of the identity of the intermediates and the reactions which they undergo. "Dual e.s.r. cavity" techniques have enabled greater accuracy and precision than is nor~nally obtained when concentrations of paramagnetic species are determined by e.s.r.

Several organic glasses which are known to form trapped electrons when gamma irradiated at 77 °K have been irradiated at 4.2 °K and examined by electron spin resonance (e.s.r.) at the same temperature. In each case an absorption is observed which is probably due to trapped electrons. In three cases, the yield of trapped electrons at 4.2 °K seems to be as great as at 77 °K. In one case, a glassy alkane, the yield is enhanced at 4.2 °K. Trapped electrons in ethanol give a narrower e.s.r. line at 4.2 °K than at 77 °K, suggesting less orientation in the solvent cage.Trapped hydrogen atoms are not detected after irradiation at 4.2 °K. Contrary to prediction, hydrogen atoms are also not detected after post-irradiation photolysis of the trapped electrons.The results suggest that electron traps exist prior to irradiation and that molecular orientation via electronic dipole interaction is not a necessary condition for electron trapping. The results do not distinguish between trapping in solvent defects or trapping via electron-induced polarization of molecular orbitals.

2-Methyltetrahydrofuran (MTHF) traps electrons and free radicals or radical-ions when irradiated with gamma rays a t 77.5 OK. The e.s.r. difference spectrum technique has been used to determine the microwave saturation properties and line shape parameters of the absorption due to "trapped" electrons. These measurements support the postulate that physically trapped electrons are present and indicate that trapped electrons and free radicals or radical-ions exist in local concentrations which are considerably greater than their average concentration in the sample. I t is concluded that they are trapped in clusters. A study of the thermal decay of the trapped electrons supports the cluster model.

The technique of measuring e.s.r. difference spectra has been extended to 77 "I<. This enables elimination of the main signal due to irradiated silica sample tubes and of about 90% of the hydrogen atom signal from the same source. Under certain conditions, e.g. when the e.s.r. spectrum due to one species can be photochemically bleached, the method permits resolution of two superimposed spectra. This has been demonstrated by measurements which resolve the e.s.r. singlet due to trapped electrons in irradiated tetrahydro-2-methylfuran from the underlying septet. These develop~~lents have rendered the e.s.r. difference method very useful for the study of paramagnetic species formed in systems which have been 7-irradiated a t 77 'I<.

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