Irradiation-driven fragmentation and chemical transformations of molecular systems play a key role in nanofabrication processes where organometallic compounds break up due to the irradiation with focused particle beams. In this study, reactive molecular dynamics simulations have been performed to analyze the role of the molecular environment on the irradiation-induced fragmentation of molecular systems. As a case study, we consider the dissociative ionization of iron pentacarbonyl, Fe(CO)5, a widely used precursor molecule for focused electron beam-induced deposition. In connection to recent experiments, the irradiation-induced fragmentation dynamics of an isolated Fe(CO)5+ molecule is studied and compared with that of Fe(CO)5+ embedded into an argon cluster. The appearance energies of different fragments of isolated Fe(CO)5+ agree with the recent experimental data. For Fe(CO)5+ embedded into an argon cluster, the simulations reproduce the experimentally observed suppression of Fe(CO)5+ fragmentation and provide an atomistic-level understanding of this effect. Understanding irradiation-driven fragmentation patterns for molecular systems in environments facilitates the advancement of atomistic models of irradiation-induced chemistry processes involving complex molecular systems.

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• Journal Article MeSH

Clusters in molecular beam experiments can mimic aerosol nanoclusters and provide molecular-level details for various processes relevant to atmospheric aerosol research. Aerosol nanoclusters, particles of sizes below 10 nm, are difficult to investigate in ambient atmosphere and thus represent a gap in our understanding of the new particle formation process. Recent field measurements and laboratory experiments are closing this gap; however, experiments with clusters in molecular beams are rarely involved. Yet, they can offer an unprecedented detailed insight into the processes including particles in this size range. In this Perspective, we discuss several up-to-date molecular beam experiments with clusters and demonstrate that the investigated clusters approach aerosol nanoclusters in terms of their complexity and chemistry. We examine remaining gaps between atmospheric aerosols and clusters in molecular beams and speculate about future experiments bridging these gaps.

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• Journal Article MeSH
• Review MeSH

The uptake of molecules on nanometer-size clusters of polyaromatic hydrocarbons (PAHs) is important for the condensation of water on PAH aerosols in the atmosphere and for ice mantle growth on nanoparticles in the interstellar medium. We generate benzene clusters BzN of mean size N̅ ≈ 300 (radius R̅ ≈ 2.2 Å) as a model system for the PAH nanoparticles. Using molecular beams and mass spectrometry detection, we investigate the uptake of water, methanol, and ethanol by these clusters. All picked up molecules are highly mobile on BzN and generate clusters within <3 ms. The relative uptakes for the different investigated molecules can be directly compared and quantified. Water molecules exhibit the lowest relative pickup probability that is ∼30% lower than those for methanol and ethanol, which are approximately the same.

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THIS REVIEW SUMMARIZES SOME RECENT EXPERIMENTS WITH ICE NANOPARTICLES (LARGE WATER CLUSTERS) IN MOLECULAR BEAMS AND OUTLINES THEIR ATMOSPHERIC RELEVANCE: (1) Investigation of mixed water-nitric acid particles by means of the electron ionization and sodium doping combined with photoionization revealed the prominent role of HNO3 molecule as the condensation nuclei. (2) The uptake of atmospheric molecules by water ice nanoparticles has been studied, and the pickup cross sections for some molecules exceed significantly the geometrical sizes of the ice nanoparticles. (3) Photodissociation of hydrogen halides on water ice particles has been shown to proceed via excitation of acidically dissociated ion pair and subsequent biradical generation and H3O dissociation. The photodissociation of CF2Cl2 molecules in clusters is also mentioned. Possible atmospheric consequences of all these results are briefly discussed.

• Keywords
• aerosols, atmospheric chemistry, molecular beams, molecular dynamics, photochemistry, photodissociation, water clusters,
• Publication type
• Journal Article MeSH
• Review MeSH