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How can light break apart a molecule trapped inside a cluster?
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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.
Light can break apart a molecule trapped within a cluster through a process known as photolysis, where the absorption of light of a sufficiently short wavelength provides the energy necessary to induce dissociation.12
When a molecule is captured inside a cluster of nonreactive atoms or molecules, the surrounding environment acts as a cage. The outcome of this light-induced breakup depends on the density of that cage:
- Incomplete Cages: If the cluster contains only a few surrounding atoms or molecules, the fragments produced by the dissociation can escape their initial cage. If the light energy is high enough, at least one of these fragments will successfully leave the cluster.2
- Complete Cages: If the cluster provides enough nonreacting atoms or molecules to form at least one complete shell around the target molecule, the cage typically holds the fragments in close proximity. This confinement often prevents the fragments from escaping, causing them to eventually recombine.2
This process highlights the unique chemical properties of clusters, which serve as a bridge between molecular and bulk matter.2