Hot and Solid Gallium Clusters: Too Small to Melt

Abstract

A novel multicollision induced dissociation scheme is employed to determine the energy content for mass-selected gallium cluster ions as a function of their temperature. Measurements were performed for $\mathrm{G}\mathrm{a}_n{}^{+}$ ($n=17$ 39, and 40) over a 90–720 K temperature range. For $\mathrm{G}\mathrm{a}_{39}{}^{+}$ and $\mathrm{G}\mathrm{a}_{40}{}^{+}$ a broad maximum in the heat capacity—a signature of a melting transition for a small cluster—occurs at around 550 K. Thus small gallium clusters melt at substantially above the 302.9 K melting point of bulk gallium, in conflict with expectations that they will remain liquid to below 150 K. No melting transition is observed for $\mathrm{G}\mathrm{a}_{17}{}^{+}$.