Max S. Matheson

Paramagnetic Species Produced by γ Irradiation of Organic Compounds

Some alkanes, olefins, alcohols, ethers, and a few other organic compounds have been irradiated with Co60 γ rays at low temperatures. The frozen irradiated samples have been examined for paramagnetic resonance, and the observed spectra in several cases have been identified with specific radicals. The methyl, ethyl, and allyl radicals are among those identified. The results in each case have been considered in relation to the present knowledge of the radiation chemistry of the compound. The mode of radical formation in many cases appears to be quite specific. Thus, in normal alkanes the major process for radical formation is by loss of a specific H atom. Hyperconjugation is used to interpret the resonance spectra.

DETECTION OF SHORT-LIVED TRANSIENTS IN RADIATION CHEMISTRY

Transients in solutions irradiated with a 5- ation sec pulse of 15-Mev electrons (av. current = 0.1 amp) were observed by means of synchronized flash absorption spectroscopy. The following solutions were studied: 0.01 M benzyl chloride in cyclohexane, 0.01 M allyl chloride (aq), 0.01 M allyl alcohol (aq), 0.004 M 1,4-cyclohexadiene in cyclohexane, 0.007 M Kl (aq), and 0.04 M KBrO/sub 3/ (aq). The absorption spectra of the transients in these solutions and their interpretion are given. (D.L.C.)

The Decomposition of Nitrate Crystals by Ionizing Radiations

Sodium nitrate, potassium nitrate, and potassium chlorate have been exposed two to four weeks in the experimental thimble of the Argonne Heavy Water Pile. After exposure these salts evolve a gas when dissolved in water or when melted or heated to a crystal transition point. The gas yields are in sodium nitrate ca 0.3, in potassium nitrate ca 0.8, and in potassium chlorate 2.0–3.0 molecules gas/100 ev. For the nitrates this gas has been shown to be largely oxygen which is trapped during irradiation in the gaseous form in small pockets in the crystal. This conclusion is based on the paramagnetism of the irradiated crystals, on chemical analysis of the evolved gases, and on measurements of the amounts of gas liberated in crushing experiments. When irradiated crystals are heated below the melting point, the gas pockets grow and coalesce, this being accompanied by a decrease in crystal density. In irradiated nitrates, oxygen and nitrite ion are formed in equivalent amounts. Experiments with low energy x‐rays i...

Paramagnetic Species in Gamma‐Irradiated Ice

The paramagnetic resonance spectra of H2O and D2O ice irradiated at 77°K have been examined. The absorbing species have been identified as H and OH (or D and OD), a significant result for the radiation chemistry of aqueous solutions. The yield of radical pairs/100 ev is about 0.14. The hyperfine splittings of the H doublet and D triplet are a factor of 16 less than are observed in the gas phase. This result is attributed to the effect of the solid on the electronic state of the H or D atoms. The spectra of H2O2 in H2O and D2O2 in D2O irradiated at 77°K support the identification of OH (or OD) absorption. In annealing experiments the H and OH disappear near 115°K. Results on solid ammonia and solid formic acid irradiated at 77°K are also described.

Fluorescence and Thermoluminescence of Ice

Experiments on the x‐ray excited fluorescence and thermoluminescence of pure ice and ice containing certain additives are described. The luminescent spectra are explained by a model in which the primary process is the radiative capture of electrons by impurity cations. The first‐order buildup of fluorescence and temperature dependence of luminous intensity are interpreted by the breakdown and formation of the dipole sheath surrounding the dissolved ions. From this viewpoint, the activation energy for rotation of a sheath ice dipole from the normal lattice position to the aligned configuration is calculated to be 0.07 ev. The principal trap depth determined from the glow curve is 0.32 ev, a correction for the luminous efficiency being incorporated in the calculation; the corresponding s value is 2×108 sec—1. Possible mechanisms for the first‐order thermoluminescence are given.

Paramagnetic Resonance of Gamma‐Irradiated Single Crystals of Ice at 77°K

The anisotropy of the paramagnetic resonance spectra of ice crystals irradiated and measured at 77 deg K was studied in- an effort to identify the paramagnetic species indicated by previous experiments. The doses were approximately 1021 ev/cc each, and the spectra were obtained with the c axis parallel and perpendicular to the axis of rotation, which was kept perpendicular and parallel to the static and microwave magnetic fields, respectively. The parallel run showed sixfold symmetry while the perpendicular run showed one canonical orientation with a minimum doublet separation, a maximum g value, and two mirror planes. The spectra show twelve-fold periodicity at 15 deg orientations to each mirror; the results are interpreted in terms of a cylindrically symmetric radical. Polycrystalline ice was also examined, giving two lines with sixfold symmetry in the parallel run; this result indicates the presence of H 2O+.

Photochemical Primary Process in Biacetyl Vapor at 4358 A

At 4358 A at room temperature the quantum yield for the primary dissociation of biacetyl increases with intensity. It is thus implied that the primary process is second order in some active species. By use of the rotating sector it is shown that the species responsible for this effect has a mean life close to that ascribed to an excited triplet state for biacetyl. At higher temperatures this intensity effect disappears and one of the products strongly inhibits both the phosphorescence and the primary dissociation. At these temperatures the data may best be treated by assuming that the triplet state of biacetyl undergoes a unimolecular dissociation with an activation energy of about 15 kcal.

On the existence of dielectrons in aqueous solutions

Abstract Alkaline aqueous solutions under high H 2 pressures when pulse radiolysed should favor the formation of dielectrons through the reaction e aq − + e aq − → (e 2 −2 )aq → H 2 + 2OH − . In our pulse radiolysis investigation of such solutions, no U.V. absorption, which can be attributed to the decay of e aq − , remains after the decay of e aq − . We conclude that either dielectrons scarcely absorb any light in the region where e aq − absorbs or else the dielectron is quite short-lived as compared to the lifetime of e aq − under these conditions.

Radiation Chemistry of Synthetic Waste

The yield of hydrogen from radiolysis of aqueous solutions is substantially reduced by the presence of nitrate and nitrite in the waste solutions. Nitrate is more efficient in scavenging the precursors to hydrogen than is nitrite, therefore, the latter should be maintained at higher levels if minimization of radiolytic gas production is required. Nitrate is the major scavenger for e(sub aq)(sup (minus)) and nitrite is the major scavenger for H atoms. At the concentration levels of the waste solutions some fraction of the radiation energy will be absorbed directly by the solutes, primarily the nitrate/nitrite components. Organic additive will increase the generation of hydrogen and mechanistic information is available to allow predictive modeling of trends in the rate of the generation. Physical parameters such as temperature, viscosity, and pressure will not significantly affect the gas generation relative to its generation under normal conditions. Radiolytic generation of N2O is very inefficient in the absence of organic solutes. No mechanistic information is available on its generation in the presence of organic additives. At the concentration levels of the inorganic salts in the waste solutions, it will be very difficult to find a chemical additive that could efficiently reduce the yield of the generated hydrogen, except, perhaps, increasing the concentration of the nitrite/nitrate components.

Radiolytic studies of reactions in the Zn+ + Mn(III) system(1)

Abstract Radiolysis of appropriate concentrations of ZnSO4 and MnSO4 in nearly neutral aqueous solutions gives closely similar amounts of Zn+ and Mn(III). Pulse radiolysis of ZnSO4 + MnSO4 solutions was used to investigate the reaction mechanism of these species, and unknown rate constants (e.g. k( Zn + + Mn(III) = 2.4 ± 0.4 × 10 9 M -1 S -1 ) were determined. Some of the Zn+ react with each other to produce Zn0 and ultimately H2, while a fraction of the Mn(III) forms a precipitate and a corresponding amount of H3O+ [G(H2) ∼ 1 was measured in the γ-irradiation of ZnSO4 + MnSO4 solutions]. This formation of gas and precipitate in an initially homogenous system provides a mechanism, whereby a fraction of the redox intermediates escape back reaction. Consequently, chemical storage of some of the energy in the redox system is made possible. The kinetics of precipitate formation were studied and indicate that nucleation is initiated by Mn(III). The effects of concentration, dose and dose-rate on H2 and MnO2 precipitate yields in γ-radiolysis are discussed. The manganese, in the precipitate in γ-radiolyses, showed an average valence of 3.65.