Dissociation of Gas Phase Ions of Atomically Precise Silver Clusters Reflects Their Solution Phase Stability

We report an attempt to probe into the energy demand of the fragmentation of atomically precise silver clusters using collision induced dissociation mass spectrometry. Energy resolved collisions of several gas phase ions of clusters, Ag₂₉(S₂R)₁₂, Ag₂₅(SR)₁₈, and Ag₄₄(SR)₃₀, reveal distinct fragmentation kinetics involving charge separation. The fragmentation pattern of [Ag₂₅(SR)₁₈]⁻ is found to be different from its structural analog, [Au₂₅(SR)₁₈]⁻. Survival yield analysis has been used to establish a direct comparison between the stability of the ions of these clusters, which reveals that [Ag₂₉(S₂R)₁₂]^3– is the most stable cluster ion, followed by [Ag₂₅(SR)₁₈]⁻ and [Ag₄₄(SR)₃₀]^4–. Gas phase stabilities reflect their solution phase stabilities, indicating that the molecular nature of the clusters is retained in the gas phase, too. We further report that fragmentation occurs in a stepwise fashion, conserving the closed shell electronic stability of the parent ion at each step. Such studies are important in understanding the electronic and geometric stability of cluster ions and their fragments.