Cluster Ion Chemistry in Gas Phase Environments

Cluster ion chemistry in the gas phase explores the formation, structure and reactivity of molecular aggregates bearing net charge under isolated conditions. Such clusters, typically generated in supersonic expansions or molecular beams and ionised by electrons or photons, serve as model systems for fundamental processes in atmospheric, interstellar and plasma environments. The interplay between solvation, electrostatic forces and quantum effects gives rise to size- and composition-dependent phenomena such as proton transfer, charge delocalisation and electron-driven dissociation. Studies combine mass spectrometry, spectroscopic interrogation and theoretical methods to elucidate reaction pathways, binding energetics and the evolution of cluster structure upon energy uptake. Insights gleaned from gas-phase cluster ions inform our understanding of aerosol nucleation, heterogeneous chemistry on ice particles and the survival of fragile species in interstellar space. The controlled isolation of individual clusters enables the dissection of stepwise reactions and provides benchmarks for models of complex systems. Emerging themes include the role of electron attachment in triggering intracluster chemistry, the influence of mixed composition on reaction kinetics and the transition from molecular aggregates to bulk-like behaviour as cluster size increases. Practical applications span from tracing pollutant transformations in the atmosphere to designing novel materials via cluster-assembly approaches.

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Cluster Ion Chemistry in Gas Phase Environments publication trend

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Technical terms

Cluster ion: A small aggregate of molecules or atoms bearing a net positive or negative charge, studied under isolated gas-phase conditions.

Molecular beam: A collimated stream of neutral or ionised particles generated by expansion into vacuum, allowing control over cluster size and internal energy.

Pickup cross section: An effective area representing the probability that a gas-phase cluster will capture a passing molecule in a molecular beam experiment.

Electron attachment: A process in which a free electron binds to a neutral cluster, often initiating intracluster reactions or dissociation pathways.

Proton transfer: The movement of a proton (H⁺) from one molecular site to another within a cluster, a key step in acid–base chemistry under isolated conditions.

Metastable decay: The delayed unimolecular dissociation of an ionised cluster, monitored in time-of-flight or reflectron mass spectrometry to infer binding energies and excitation dynamics.

References

1. Pickup and reactions of molecules on clusters relevant for atmospheric and interstellar processes. Physical Chemistry Chemical Physics (2021).
2. Does HNO 3 dissociate on gas-phase ice nanoparticles?. Physical Chemistry Chemical Physics (2023).
3. Metastable Evaporation of Molecules from Water Clusters. The Journal of Physical Chemistry A (2024).