Transient and Stable Silver Clusters Induced by Radiolysis in Methanol

Abstract

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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