Decay channels and appearance sizes of doubly anionic gold and silver clusters

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Second electron affinities of Auₙ and Agₙ clusters and the dissociation energies for fission of the Auₙ²⁻ and Agₙ²⁻ dianions are calculated using the finite-temperature shell-correction method and allowing for triaxial deformations. Dianionic clusters with N > 2 are found to be energetically stable against fission, leaving electron autodetachment as the dominant decay process. The second electron affinities exhibit pronounced shell effects in excellent agreement with measured abundance spectra for Auₙ²⁻ (N < 30), with appearance sizes N=12 for gold dianionic clusters and N=24 for silver dianionic clusters.