Photoionization energies of small photolytic silver microclusters (Ag
2, Ag
3, and Ag
4) can be determined from the threshold photon energies that are required to induce the photobleach of the clusters. The principle of the measurement is described along with some typical results. The threshold energies were measured as approximately 1.6, 0.7, and 1.1 eV, for Ag
2, Ag
3, and Ag
4, respectively. They exhibit an obvious even-odd oscillatory trend of the ionization energy, characteristic of small metal clusters, as well as a strong influence of the interaction with silver bromide grain surface. We also discuss how the present results or the quantum size effects influence the processes of latent image formation and photographic development, in relation to our earlier observations with respect to the relative redox stabilities of the clusters.
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