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The optical absorption spectra of Ag 0 , Ag 2 + , transient oligomers, and stable clusters were studied in deaerated methanol by pulse and γ-radiolysis methods and compared with data obtained from studies using other solvents. From the decay of esolv at 620 nm, the formation rate constant of Ag 0 was determined to be k(esolv + Ag + ) ) (2.6 ( 0.6) × 10 10 M -1 s -1 . The coalescence rate of transient oligomers is particularly slow and the growth process is not completed within 2 s after the pulse. The surface plasmon band of stable clusters obtained by γ-radiolysis in methanol is intense and sharp ( 385 nm ) 1.8 × 10 4 M -1 cm -1 ). The clusters are readily oxidized by oxygen. By adding methyl viologen MV 2+ to the solution containing stable silver clusters, the blue color of MV +• is transitorily observed, and the small clusters are developed into larger ones. Similarly, by pulse radiolysis of a mixture of silver cations and MV 2+ , silver atoms and MV +• are formed immediately through solvated electron scavenging, but subsequently additional MV +• are produced by reduction of MV 2+ by Ag 0 and small oligomers. In a further step, MV +• radicals reduce Ag + cations adsorbed on large clusters and let them develop eventually to larger sizes. The general mechanism of the methanol radiolysis is revisited on the basis of electron and radical scavenging by Ag + and silver clusters, and values of the yields of methanol radiolysis species are discussed in detail.

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The detailed kinetics of the multistep mechanism of the Au(III) ion reduction into gold clusters have been investigated by radiation chemistry methods in 2-propanol. In particular, a discussion on the steady state radiolysis dose-dependence of the yields concludes to a comproportionation reaction of nascent gold atoms Au(0) with excess Au(III) ions into Au(II) and Au(I). This reaction should be achieved through Au(III) consumption before the coalescence of atoms Au(0) into gold clusters may occur. Then gold clusters catalyze the reduction of Au(I) by 2-propanol. It was also found that a long-lived Au(II) dimer, (Au(II))(2), was transiently formed according to the quantitative analysis of time-resolved absorbance signals obtained by pulse radiolysis. Then the disproportionation of Au(II) is intramolecular in the dimer instead of intermolecular, as usually reported. The yields, reaction rate constants, time-resolved spectra, and molar extinction coefficients are reported for the successive one-electron reduction steps, involving especially the transient species, such as Au(II), (Au(II))(2), and Au(I). The processes are discussed in comparison with other solvents and other metal ions.

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Using the pulse radiolysis technique, studies on reactions of 3,4,5-trihydroxybenzoic acid [gallic acid (GA)] with radical species generated in water are reported. At pH 6.8 and 9.7, OH radicals react with GA to give an adduct initially with rate constants of the order of 1 ] 1010 dm3 mol~1 s~1. This adduct then reacts with parent GA molecules with rate constants of the order 5 ] 108 dm3 mol~1 s~1 to give phenoxyl type radical species having absorption maxima in the 350 nm region. At pH 12 and 13.6, OH/O~radicals directly bring about oxidation of GA. SpeciÐc oxidants like azidyl radical bring about one electron oxidation at neutral and alkaline pHs with almost di †usion controlled rate constants. Rate constants for the reaction of radicals Br 2 ãre found to be lower than those for OH radicals by an order of magnitude. At pH 0, both OH and Cl 2 radicals react with GA to give phenoxyl type radicals. The phenoxyl radicals formed are quite stable at higher pHs, which make GA a good antioxidant. Rate constants for the reactions of with di †erent protolytic e aq forms of GA are determined.

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