ESR Evidence on Trapped Electrons and ``CO2−'' in γ-Irradiated 3-Methylpentane

Abstract

The singlet ESR signal of γ-irradiated 3-methylpentane (3-MP) glass [K. Tsuji, H. Yoshida, and K. Hayashi, J. Chem. Phys. 46, 810 (1967)], which is attributable to physically trapped electrons, and the singlet and doublet resulting from reaction of electrons with CO2 [P. M. Johnson and A. C. Albrecht, J. Chem. Phys. 44, 1845 (1966)] in 3-MP glass have been examined further. Immediately after production by a 1019-eV g−1, 5-min γ dose, the electron line decays with an apparent half-life of less than 20 min. It is readily removed by illumination at 13 500 Å. ESR saturation is significant at 10−3 mW and prevents detection of the signal at powers above ∼1 mW. The ESR g value and the radiation G value are estimated to be ∼2.002 and 0.5±0.2, respectively. When 3-MP or 2-methyl-pentene-1 (2-MP-1) containing CO2 is γ irradiated at 77°K, a singlet (g=∼2.0007; linewidth=∼3.1 G) and a flanking doublet with a splitting of ∼8 G are produced. The singlet, but not the doublet, shows saturation effects starting at ∼0.05 mW. It may be removed by illumination of the sample at wavelengths of 4800 Å and below, producing new species, but is unaffected at 5500 Å and above. The initial ratio of the singlet to the doublet, the growth on standing at 77°K, and the rate of bleaching with ultraviolet light are sensitive to the amount of CO2 present. The observed radiation G value in samples containing 1 mole % CO2 and 99 mole % 3-MP, with a vapor—solid ratio of 8, is ∼0.3. The spectra are the same as those produced (Johnson and Albrecht) by photoionization of tetramethylparaphenylenediamine (TMPD) in 3-MP containing CO2 at 77°K.