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Why can a cluster melt while it undergoes an exothermic chemical reaction?

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cluster Figure 1: The four stable geometric structures of the seven-atom cluster of argon, in order of increasing energy: (A) A pentagonal bipyramid. (B) A regular octahedron with one face capped by the seventh atom. (C) A regular tetrahedron with three of its faces capped by other atoms. (D) A trigonal bipyramid with two of its faces capped by other atoms; although this has the highest energy of the four structures, it is very close in energy to the tricapped tetrahedron.

A cluster may melt while undergoing an exothermic chemical reaction if the reaction releases a sufficient quantity of energy to trigger a phase transition from solid to liquid.1

In the context of cluster chemistry, this process is facilitated by the unique physical properties of clusters compared to bulk matter. Because a large fraction of a cluster's particles are located on its surface, the mobility of these particles is enhanced, making it easier for the cluster to expand and undergo structural changes. Furthermore, clusters often have lower melting points than their corresponding bulk solids, sometimes melting at temperatures as low as half the bulk melting temperature. When an exothermic reaction occurs, the energy released can be enough to overcome the forces holding the solid cluster together, causing it to transition into a liquidlike state.21