Yoko Miyatake

Electronic spectra of C70 anions produced in γ-irradiated organic glasses at 77 K

Abstract The electronic spectra of C70 anions were observed in γ-irradiated methylcyclohexane and MTHF glasses at 77 K. The band at 1386 nm in methylcyclohexane was assigned to C−70. The spectrum in MTHF consisted of two bands at 1184 and 1377 nm. The former band was tentatively ascribed to C2−70. The values of ϵG obtained are 265±40, 230±45 and 217±45 M−1 cm−1 at 1386, 1377 and 1184 nm, respectively.

Comparative ESR study of C60 and C70 radical anions produced in γ-irradiated organic solid solutions at 77 K

Abstract ESR spectra of C 70 radical anions were detected for C 70 /methylcyclohexane (MCHX) and C 70 /2-methyltetrahydrofuran (MTHF) solid solutions which were γ-irradiated at 77 K and subsequently annealed at 107–117 K. The ESR spectrum for C 70 /MCHX was a singlet which was ascribed to C 70 − , and was flanked by a pair of satellites due to matrix proton spin flip lines. The ESR spectrum for C 70 /MTHF was a superposition of a singlet and a deformed doublet. The latter was unstable and disappeared at 109 K, and was tentatively ascribed to C 70 2− . ESR spectra of C 60 radical anions were partly reinvestigated and are compared to those of C 70 . The relative electron attachment efficiencies for C 60 and C 70 at 77 K were estimated, and the former was about twice as large as the latter. Isothermal decay at 77 K was observed for both C 60 and C 70 radical anions.

Emission and excitation spectra of silver atoms in γ-irradiated aqueous, ethanol, and 2-methyltetrahydrofuran solutions at 77 K

Abstract Silver atoms (Ag°) were produced by γ-irradiation of frozen aqueous, ethanol and 2-methyltetrahydrofuran (MTHF) solutions containing Ag+ at 77 K. Emission and excitation spectra of Ag° were measured at this temperature for these solutions. Aqueous solutions did not emit appreciably. Ethanol and MTHF solutions showed two emission bands centered at nearly 500 and 600 nm, which had short and long lifetimes, respectively. The intensity ratios for the two bands, i.e. I500/I600 were found to decrease with increasing excitation wavelength. The excitation spectra of Ag° in ethanol at 77 K showed that the threshold wavelengths for both emission bands are 360 nm. However, the threshold wavelengths for 500 and 600 nm bands are 360 and 400 nm, respectively, in MTHF. The ionization potentials of Ag° in these solutions were estimated from the Born equation. The observed results can be explained in terms of the photoionization of excited Ag°, and the formation of fluorescent complexes consisting of excited silver atoms and solvent molecules.

ESR spectra of C60 radical anions produced in γ-irradiated organic solid solutions at 77 K

Abstract ESR spectra of C 60 radical anions were detected for C 60 /MCHX and C 60 /MTHF solid solutions which were γ-irradiated at 77 K and subsequently annealed at 110–140 K. The g -factors were 2.0019 and 1.9997 for C 60 /MCHX (or C 60 /MCHX- d 14 ) and C 60 /MTHF, respectively. Δ H pp = 0.26 mT was obtained for those solutions and was smaller than the values reported for electrolytically produced C 60 − by about 50%. Matrix proton spin flip satellite lines were observed in C 60 /MCHX.

Electronic spectra of anion radicals of C60 and its derivative in γ-irradiated MTHF solid solutions

Abstract The γ-dose dependence of the absorbance of the electronic absorption bands in the near-IR region of the anion radicals produced in MTHF solid solution containing C 60 at 77 K was investigated. The bands at λ max =1075 and 950 nm were ascribed to C 60 − and C 60 2− anion radicals, respectively. In the case of the solid solution containing [5,6]-bis(4-methoxyphenyl)methano[60]fullerene, which was used as a C 60 derivative, the bands at λ max =1075 and 1140 nm were ascribed to the mono-anion, and the band at λ max =1025 nm to the di-anion radical of the C 60 derivative. It is inferred that the unpaired electron density is delocalized on the C 60 moiety with a slight perturbation from the [5,6]-bis(4-methoxyphenyl)-methane functionality.

Optical and ESR studies of radiolytically reduced species of Ag(I) complexes in organic solid solutions at 77 K

Abstract Ag(I) complexes in ethanol and 2-methyltetrahydrofuran solid solutions were reduced by γ-irradiation at 77 K. The hyperfine coupling constants due to silver observed in the ESR spectra of the reduction products indicate that the excess electron is localized mainly on the 5s orbital of the silver atoms for Ag(I)–β-diketones but not for Ag(I) complexes coordinated with nitrogen atoms in either solid. It has been found that the isotropic hyperfine coupling constants of Ag 0 in Ag(0)–β-diketones depend on the solvent.

ESR study on gold atoms produced in γ-irradiated MTHF and 10 M NaOH aqueous solutions containing Au+ ions at 77 K

Abstract MTHF and 10 M NaOH aqueous solutions containing Au + ions were γ-irradiated at 77 K. ESR measurements at 73 K revealed the production and trapping of Au 0 atoms in the solid solutions. This is the first ESR report of Au 0 atoms which are produced radiation–chemically by reducing Au + ions. The g J and hyperfine splitting values of Au 0 atoms were determined.