| 1. |
- Gatchell, Michael, et al.
(författare)
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Complexes of gold and imidazole formed in helium nanodroplets
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:11, s. 7739-7745
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Tidskriftsartikel (refereegranskat)abstract
- We have studied complexes of gold atoms and imidazole (C3N2H4, abbreviated Im) produced in helium nanodroplets. Following the ionization of the doped droplets we detect a broad range of different Au(m)Im(n)(+) complexes, however we find that for specific values of m certain n are magic and thus particularly abundant. Our density functional theory calculations indicate that these abundant clusters sizes are partially the result of particularly stable complexes, e.g. AuIm(2)(+), and partially due to a transition in fragmentation patterns from the loss of neutral imidazole molecules for large systems to the loss of neutral gold atoms for smaller systems.
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| 2. |
- Gatchell, Michael, et al.
(författare)
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Magic sizes of cationic and protonated argon clusters
- 2018
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 98:2
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Tidskriftsartikel (refereegranskat)abstract
- There has long been a discrepancy between the size distributions of Ar-n(+) clusters measured by different groups regarding whether or not magic numbers appear at sizes corresponding to the closure of icosahedral (sub-) shells. We show that the previously observed magic cluster size distributions are likely the result of an unresolved ArnH+ component, i.e., from protonated argon clusters. We find that the proton impurity gives cluster geometries that are much closer to those for neutral rare-gas clusters, which are known to form icosahedral structures, than for the pure cationic clusters, explaining why the mass spectra from protonated argon clusters better matches these structural models. Our results thus show that even small impurities, e.g., a single proton, can significantly influence the properties of clusters.
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| 3. |
- Goulart, Marcelo, et al.
(författare)
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The adsorption of helium atoms on small cationic gold clusters
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:14, s. 9554-9560
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Tidskriftsartikel (refereegranskat)abstract
- Adducts formed between small gold cluster cations and helium atoms are reported for the first time. These binary ions, Aun+Hem, were produced by electron ionization of helium nanodroplets doped with neutral gold clusters and were detected using mass spectrometry. For a given value of n, the distribution of ions as a function of the number of added helium atoms, m, has been recorded. Peaks with anomalously high intensities, corresponding to so-called magic number ions, are identified and interpreted in terms of the geometric structures of the underlying Au-n(+) ions. These features can be accounted for by planar structures for Au-n(+) ions with n <= 7, with the addition of helium having no significant effect on the structures of the underlying gold cluster ions. According to ion mobility studies and some theoretical predictions, a 3-D structure is expected for Au-8(+). However, the findings for Au-8(+) in this work are more consistent with a planar structure.
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| 4. |
- Kranabetter, Lorenz, et al.
(författare)
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Considerable matrix shift in the electronic transitions of helium-solvated cesium dimer cation Cs2He+n
- 2019
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:45, s. 25362-25368
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the photodissociation of helium-solvated cesium dimer cations using action spectroscopy and quantum chemical calculations. The spectrum of Cs2He+ shows three distinct absorption bands into both bound and dissociative states. Upon solvation with further helium atoms, considerable shifts of the absorption bands are observed, exceeding 0.1 eV (850 cm(-1)) already for Cs2He10+, along with significant broadening. The shifts are highly sensitive to the character of the excited state. Our calculations show that helium atoms adsorb on the ends of Cs-2(+). The shifts are particularly pronounced if the excited state orbitals extend to the area occupied by the helium atoms. In this case, Pauli repulsion leads to a deformation of the excited state orbitals, resulting in the observed blue shift of the transition. Since the position of the weakly bound helium atoms is ill defined, Pauli repulsion also explains the broadening.
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| 5. |
- Laimer, Felix, et al.
(författare)
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Highly Charged Droplets of Superfluid Helium
- 2019
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 123:16
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Tidskriftsartikel (refereegranskat)abstract
- We report on the production and study of stable, highly charged droplets of superfluid helium. Using a novel experimental setup we produce neutral beams of liquid helium nanodroplets containing millions of atoms or more that can be ionized by electron impact, mass-per-charge selected, and ionized a second time before being analyzed. Droplets containing up to 55 net positive charges are identified and the appearance sizes of multiply charge droplets are determined as a function of the charge state. We show that the droplets are stable on the millisecond timescale of the experiment and decay through the loss of small charged clusters, not through symmetric Coulomb explosions.
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| 6. |
- Martini, Paul, et al.
(författare)
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Atomic Gold Ions Clustered with Noble Gases : Helium, Neon, Argon, Krypton, and Xenon
- 2019
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 123:44, s. 9505-9513
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution mass spectra of helium droplets doped with gold and ionized by electrons reveal HenAu+ cluster ions. Additional doping with heavy noble gases results in NenAu+, ArnAu+, KrnAu+, and XenAu+ cluster ions. The high stability predicted for covalently bonded Ar2Au+, Kr2Au+, and Xe2Au+ is reflected in their relatively high abundance. Surprisingly, the abundance of Ne2Au+, which is predicted to have zero covalent bonding character and no enhanced stability, features a local maximum, too. The predicted size and structure of complete solvation shells surrounding ions with essentially nondirectional bonding depends primarily on the ratio sigma* of the ion-ligand versus the ligand-ligand distance. For Au+ solvated in helium and neon, the ratio sigma* is slightly below 1, favoring icosahedral packing in agreement with a maximum observed in the corresponding abundance distributions at n = 12. HenAu+ appears to adopt two additional solvation shells of I-h symmetry, containing 20 and 12 atoms, respectively. For ArnAu+, with sigma* approximate to 0.67, one would expect a solvation shell of octahedral symmetry, in agreement with an enhanced ion abundance at n = 6. Another anomaly in the ion abundance at Ar9Au+ matches a local maximum in its computed dissociation energy.
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