Oxidation Kinetics of Large Photolytic Silver Clusters in Redox Buffer Solutions

Abstract

Oxidation kinetics of relatively large silver clusters, formed by the excess exposure beyond the shoulder region of characteristic curves, in redox buffer solutions was elucidated by investigating the effects of the redox potential and silver ion activity of the buffer solution on the oxidation rates of various size silver clusters. A single-step oxidation of Ag_n cluster proceeds via the electron transfer front Ag_n to the buffer solution and the subsequent release of a silver ion from Ag_n⁺ to produce Ag_n-1, and Ag⁺ . The ionization potential of Ag_n and the dissociation energy of Ag_n⁺ to Ag_n-1, and Ag⁺ are the dominant factors inlluettcing the rate of the oxidation. It was concluded that the ionization potential is decreased with cluster size while the dissociation energy has the reverse trend. The trend can be predicted from the classical electromagnetics and thermodynamics and is also consistent with the results of various molecular orbital calculations on metal clusters. The kinetics of the single-step oxidation is discussed in detail in terms of free energy vs. reaction coordinate diagrams on the basis of such trends of the energy states of the photolytic silver clusters.