Abstract
Formation and growth of neutral SO2 clusters is investigated in an adiabatic-expansion setup by means of sulfur 2p (S2p) photoelectron spectroscopy and theoretical modeling. The shift in S2p ionization energy between the cluster and a single molecule, i.e., IE(cluster)-IE(monomer), is recorded and used to monitor the mean cluster size over a wide range of expansion conditions. The produced clusters were shown to fall into two different size regimes. Comparison between theoretical simulations and experimental observations suggests that while the smallest clusters belong to the ultrafine particle mode and have a liquid-like structure, the larger clusters belong to the accumulation mode of fine particles and possibly have a frozen cluster core. The transition between the two size/structure regimes occurs over a narrow interval in expansion conditions and may possibly reflect a change in growth mechanism from monomer addition to growth by cluster-cluster collisions.(c) Jarle Harnes, Mahmoud Abu-Samha, Mathias...
Highlights
Clusters are aggregates of atoms and molecules, containing from a few to millions of building units (Johnston 2002) and ranging in size from less than a nanometer to the lower-micron scale (Finlayson-Pitts 2009)
The resulting beam of clusters and uncondensed monomers was subsequently probed by sulfur 2p (S2p) photoelectron spectroscopy; see Figure 2 for a representative spectrum
It is convenient to use the monomer line for internal reference, and we will focus on the mean cluster–monomer shift in S2p3=2 ionization energy (DIE)
Summary
Clusters are aggregates of atoms and molecules, containing from a few to millions of building units (Johnston 2002) and ranging in size from less than a nanometer to the lower-micron scale (Finlayson-Pitts 2009). In this very concrete sense, clusters bridge the gap between atoms and molecules and the condensed phases. Clusters often possess properties different from those of their constituent building blocks and different from the corresponding condensed phases.
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