Recent lab and field measurements have indicated critical roles of organic acids in enhancing new atmospheric aerosol formation. Such findings have stimulated theoretical studies with the aim of understanding the interaction of organic acids with common aerosol nucleation precursors like bisulfate (HSO4(-)). We report a combined negative ion photoelectron spectroscopic and theoretical investigation of molecular clusters formed by HSO4(-) with succinic acid (SUA, HO2C(CH2)2CO2H), HSO4(-)(SUA)n (n = 0-2), along with HSO4(-)(H2O)n and HSO4(-)(H2SO4)n. It is found that one SUA molecule can stabilize HSO4(-) by ca. 39 kcal/mol, three times the corresponding value that one water molecule is capable of (ca. 13 kcal/mol). Molecular dynamics simulations and quantum chemical calculations reveal the most plausible structures of these clusters and attribute the stability of these clusters to the formation of strong hydrogen bonds. This work provides direct experimental evidence showing significant thermodynamic advantage by involving organic acid molecules to promote formation and growth in bisulfate clusters and aerosols.
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We
present a joint experimental and theoretical study on double iron
atom doped germanium clusters, Fe2Ge
n
–/0 (n = 3–12). The
experimental photoelectron spectra of cluster anions are reasonably
reproduced by theoretical simulations. The low-lying structures of
the iron-doped semiconductor clusters are obtained by using an ab
initio computation-based genetic-algorithm global optimization method.
We find that the smaller-sized Fe2Ge
n
– (n = 3–8) clusters
adopt bipyramid-based geometries, while the larger ones (n ≥ 9) adopt polyhedral cagelike structures with one interior
Fe atom. Interestingly, starting from n = 8, the
most stable anionic clusters Fe2Ge
n
– exhibit structures that are different from
that of their neutral counterparts Fe2Ge
n
. Robust ferromagnetic interaction is found between the two
doped iron atoms in the neutral clusters Fe2Ge
n
, while the total spin moment always remains at 4
μB for all the neutral double iron atom doped germanium
clusters up to n = 12. This behavior is in stark
contrast to the magnetic quenching behavior typically observed in
germanium clusters doped with a single Fe atom.
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