Chapter 11
Cluster Dissociation, Intracluster
Reactivity and Effect of the Ligands
The physical properties of small metal clusters, such as ionization potentials, electron affinities, and dissociation energies, are largely different from those of the bulk
materials. Theoretical calculations have suggested that small clusters have closepacked structures but that their stabilities change dramatically with the cluster sizes.
Cluster size distributions based on mass spectrometry and fragmentation patterns
provide information on particularly stable clusters; however, it is difficult to measure
the dissociation energies as a function of cluster sizes. Early studies of cluster
dissociation retrospect to 1980s, such as the one by Gingerirch [1] using conventional Knudsen cell techniques. Following that, cluster thermal dissociation [2–6],
photodissociation (or laser-induced dissociation) [7–18] and collision-induced dissociation (CID) [19–38] have been extensively and meticulously studied, enabling the
measurement of cluster dissociation energies. From analysis of internal cluster structure and fragmentation dynamics relating to total energy and electron population, it
is discerned that the regimes of system evolution are associated with a few processes,
including energy transfer/accumulation (by photo excitation or thermal treatment or
enough collisions), contingent isentropic expansion, dynamical fragment formation
with energy thresholds, de-excitation and thermalization. The spontaneous structural
relaxation of metal clusters, driven by thermal/collision or photoexcitation [33], could
not only induce direct fragmentation/dissociation but also give rise to intracluster
redox reactions with size-dependent branching ratios, especially for transition-metal
involved clusters which possess different valence states (or oxidation states) and
varied charge distribution of the atoms in the cluster [34].
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
Z. Luo and S. N. Khanna, Metal Clusters and Their Reactivity,
https://doi.org/10.1007/978-981-15-9704-6_11
175
Cluster Dissociation, Intracluster
Reactivity and Effect of the Ligands
The physical properties of small metal clusters, such as ionization potentials, electron affinities, and dissociation energies, are largely different from those of the bulk
materials. Theoretical calculations have suggested that small clusters have closepacked structures but that their stabilities change dramatically with the cluster sizes.
Cluster size distributions based on mass spectrometry and fragmentation patterns
provide information on particularly stable clusters; however, it is difficult to measure
the dissociation energies as a function of cluster sizes. Early studies of cluster
dissociation retrospect to 1980s, such as the one by Gingerirch [1] using conventional Knudsen cell techniques. Following that, cluster thermal dissociation [2–6],
photodissociation (or laser-induced dissociation) [7–18] and collision-induced dissociation (CID) [19–38] have been extensively and meticulously studied, enabling the
measurement of cluster dissociation energies. From analysis of internal cluster structure and fragmentation dynamics relating to total energy and electron population, it
is discerned that the regimes of system evolution are associated with a few processes,
including energy transfer/accumulation (by photo excitation or thermal treatment or
enough collisions), contingent isentropic expansion, dynamical fragment formation
with energy thresholds, de-excitation and thermalization. The spontaneous structural
relaxation of metal clusters, driven by thermal/collision or photoexcitation [33], could
not only induce direct fragmentation/dissociation but also give rise to intracluster
redox reactions with size-dependent branching ratios, especially for transition-metal
involved clusters which possess different valence states (or oxidation states) and
varied charge distribution of the atoms in the cluster [34].
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Singapore Pte Ltd. 2020
Z. Luo and S. N. Khanna, Metal Clusters and Their Reactivity,
https://doi.org/10.1007/978-981-15-9704-6_11
175