Kozo Tsuji

ESR Study of Irradiated Pyridine

Pyridine and pyridine‐d5 were irradiated with electrons in the solid state at −196°C. After the irradiation, ESR spectra were measured over a temperature range from −196°C to their melting points. For pyridine, a triplet spectrum (separation of 30 G) with a quartet substructure (separation of 4.3 G) was observed at −196°C. It was assigned to cation radicals [Complex chemical formula] The triplet spectrum disappeared at elevated temperatures and an eight‐line spectrum (separation of 12 G) was observed at −90°C which was assigned to free radicals [Complex chemical formula] After the disappearance of these radicals at −65°C, a singlet spectrum (ΔHmsl of 15 G) was observed and disappeared at about −50°C. It was assigned to pyridyl radicals. The radicals produced in the irradiated pyridine‐d5 had the same nature as those observed in irradiated pyridine.

Electron spin resonance and optical studies of radiation-induced intermediates. Radical ions and radicals from α-methylstyrene in organic glasses

Radical ion and radical intermediates derived from α-methylstyrene by gamma irradiation and photoionization in organic glasses have been assigned by e.s.r. and optical techniques. Measurements made in rigid solutions of the monomer in 3-methylpentane and methyltetrahydrofuran at –196° indicate that the radical anion is formed by electron capture during irradiation and exhibits absorption bands at 411 and 580 nm. When these glasses are warmed after gamma irradiation, the radical anion is converted to the neutral α,α-dimethylbenzyl radical by proton transfer from the positive ion. The latter radical is also observed in ethanol glasses immediately after irradiation, and the hyperfine splitting constants are 16.5 gauss for the 6 methyl protons and 5.5 gauss for the 3 protons (ortho and para) in the aromatic ring. Evidence from isotopic studies indicates that the neutral radical is formed in ethanol by proton transfer from the hydroxylic proton to the vinylidene group of the radical anion.

Saturation studies of the electron spin resonance due to trapped electrons in gamma-irradiated and photo-ionized organic glasses

Relaxation times for trapped electrons in organic glasses at 77°K have been determined from the power saturation characteristics of the electron spin resonance. The spin-lattice relaxation time T1 is longer than 10–3 sec, and the spin-spin relaxation time T2 decreases with γ-irradiation dose. The saturation behaviour of a photo-ionized glass is similar to that of the corresponding γ-irradiated glass when the comparison is made at nearly the same bulk concentration of trapped electrons. Evidence for a non-uniform distribution of paramagnetic species in these irradiated glasses is critically examined, and attention is directed to difficulties of interpretation.

ESR Study on Irradiated Pyridine: Effect of Iodine Addition

When pyridine was irradiated at −196°C, the main free radical formed was the cation radical. [Complex chemical formula] The G value for the formation of the cation radical was 0.5. The addition of iodine to pyridine caused large increase in G value to as high as 13. The high G value is interpreted as due to the fact that the cation radical is produced through the excited state of the charge‐transfer complex of pyridine with iodine.