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Aqueous, 2-methyltetrahydrofuran, and ethanol solutions containing Ag+ were irradiated at 4 or 77 K with γ-rays. The main absorption bands observed in the region of 350−450 nm for these solutions are ascribed to Ag0. The absorption bands consist of several components, which are ascribed to Ag0 trapped in cavities with different structures. As the annealing temperature was raised, the bands at the shorter wavelengths became predominant in the aqueous solution. In addition to the main absorption bands, two or three absorption bands were observed in the vicinity of 300 nm for the solutions other than the aqueous solution at 77 K. In comparison with the spectra of Ag0 in solid rare gases, we tentatively ascribe the bands near 300 nm to Ag0 trapped in a large cavity in which shell structure consists of C−H groups.

EtOH and MTHF solutions containing Cu + ions are γ-irradiated at 77 K. ESR spectra are attributed, for the first time, to Cu 0 that is produced radiation-chemically by reducing Cu + ions in the solutions at 77 K. A large delocalization of the unpaired spin density of Cu 0 onto ligands is deduced. No evidence for formation of the dimer cation of Cu 0 has been obtained. This is contrary to the case of Ag 0 produced in the solutions containing Ag + ions. The NUV absorption spectrum of Cu 0 is decomposed into five Gaussian bands that are attributed to two types of exciplexes formed between excited Cu 0 and ligands: one associates with Cu + ions as well as solvent molecules, the other consists mainly of solvent molecules. The exciplexes are supposed to be transferred to relaxed states followed by two emission bands, one of which is common to both solvents and the other is characteristic of the solvents. The absorption band at 255 nm is ascribed to a photoionization spectrum of Cu 0 .

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Ethanol and 2-methyltetrahydrofuran (MTHF) solutions of silver perchlorate were irradiated with γ-rays at 77 K. Two kinds of silver atoms (Ag0) and a small amount of dimer cations (Ag2+) were formed in both solids immediately after irradiation. On storing at 77 K, both Ag0 species reacted with Ag+ to form Ag2+ in ethanol, while in MTHF only the minor Ag0 species reacted, resulting in less growth of Ag2+ yield than in ethanol. The mechanism for the formation of Ag2+ has been discussed in terms of thermal diffusion and quantum tunneling.