| 1. |
- Duensing, Felix, et al.
(författare)
-
Complexes with Atomic Gold Ions : Efficient Bis-Ligand Formation
- 2021
-
Ingår i: Molecules. - : MDPI AG. - 1431-5157 .- 1420-3049. ; 26:12
-
Tidskriftsartikel (refereegranskat)abstract
- Complexes of atomic gold with a variety of ligands have been formed by passing helium nanodroplets (HNDs) through two pickup cells containing gold vapor and the vapor of another dopant, namely a rare gas, a diatomic molecule (H-2, N-2, O-2, I-2, P-2), or various polyatomic molecules (H2O, CO2, SF6, C6H6, adamantane, imidazole, dicyclopentadiene, and fullerene). The doped HNDs were irradiated by electrons; ensuing cations were identified in a high-resolution mass spectrometer. Anions were detected for benzene, dicyclopentadiene, and fullerene. For most ligands L, the abundance distribution of AuLn+ versus size n displays a remarkable enhancement at n = 2. The propensity towards bis-ligand formation is attributed to the formation of covalent bonds in Au+L2 which adopt a dumbbell structure, L-Au+-L, as previously found for L = Xe and C-60. Another interesting observation is the effect of gold on the degree of ionization-induced intramolecular fragmentation. For most systems gold enhances the fragmentation, i.e., intramolecular fragmentation in AuLn+ is larger than in pure L-n(+). Hydrogen, on the other hand, behaves differently, as intramolecular fragmentation in Au(H-2)(n)(+) is weaker than in pure (H-2)(n)(+) by an order of magnitude.
|
|
| 2. |
- González-Lezana, Tomás, et al.
(författare)
-
Solvation of ions in helium
- 2020
-
Ingår i: International reviews in physical chemistry (Print). - 0144-235X .- 1366-591X. ; 39:4, s. 465-516
-
Forskningsöversikt (refereegranskat)abstract
- We review the solvation of atomic, molecular or cluster ions in HNDs. After briefly discussing the properties of snowballs in bulk helium we consider experimental conditions for the efficient synthesis of charged, doped HNDs. We show that the cluster ions observed in conventional mass spectrometers originate from fission of highly charged HNDs. The ionization threshold of HNDs doped with alkalis reveals the minimum cluster size required for full immersion. The abundance distributions of HeNX +/- ions frequently reveal local anomalies or magic numbers. We demonstrate that the abundance is approximately proportional to the evaporation energy. Observed and calculated magic numbers will be compiled, including data for ions solvated in molecular hydrogen. Alternative methods to forming HeNX+ that do not employ HNDs will be summarized. Electronic excitation spectra of C-60(+) and polycyclic aromatic hydrocarbon ions reveal the properties of the helium adsorption layer in quantitative detail. Next we discuss theoretical efforts to describe the interaction between ions and helium. We close with summarizing the size dependence of physical quantities computed for atomic alkali and alkaline earth cations in helium, such as binding energy, superfluid fraction, structural order, radial density profiles, and the existence of first and higher solvation shells.
|
|
| 3. |
- Goulart, Marcelo, et al.
(författare)
-
The structure of coronene cluster ions inferred from H-2 uptake in the gas phase
- 2017
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:41, s. 27968-27973
-
Tidskriftsartikel (refereegranskat)abstract
- Mass spectra of helium nanodroplets doped with H-2 and coronene feature anomalies in the ion abundance that reveal anomalies in the energetics of adsorption sites. The coronene monomer ion strongly adsorbs up to n = 38 H-2 molecules indicating a commensurate solvation shell that preserves the D-6h symmetry of the substrate. No such feature is seen in the abundance of the coronene dimer through tetramer complexed with H-2; this observation rules out a vertical columnar structure. Instead we see evidence for a columnar structure in which adjacent coronenes are displaced in parallel, forming terraces that offer additional strong adsorption sites. The experimental value for the number of adsorption sites per terrace, approximately six, barely depends on the number of coronene molecules. The displacement estimated from this number exceeds the value reported in several theoretical studies of the bare, neutral coronene dimer.
|
|
| 4. |
- Leidlmair, Christian, et al.
(författare)
-
Structures, Energetics, and Dynamics of Helium Adsorbed on Isolated Fullerene Ions
- 2012
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:7
-
Tidskriftsartikel (refereegranskat)abstract
- Helium adsorbed on C60+ and C70+ exhibits phenomena akin to helium on graphite. Mass spectra suggest that commensurate layers form when all carbon hexagons and pentagons are occupied by one He each, but that the solvation shell does not close until 60 He atoms are adsorbed on C60+, or 62 on C70+. Molecular dynamics simulations of C60Hen+ at 4 K show that the commensurate phase is solid. Helium added to C60He32+ will displace some atoms from pentagonal sites, leading to coexistence of a registered layer of immobile atoms interlaced with a nonregistered layer of mobile atoms.
|
|
| 5. |
- Martini, Paul, et al.
(författare)
-
Atomic Gold Ions Clustered with Noble Gases : Helium, Neon, Argon, Krypton, and Xenon
- 2019
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 123:44, s. 9505-9513
-
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.
|
|
| 6. |
- Martini, Paul, et al.
(författare)
-
Splashing of Large Helium Nanodroplets upon Surface Collisions
- 2021
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 127:26
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work we observe that helium nanodroplets colliding with surfaces can exhibit splashing in a way that is analogous to classical liquids. We use transmission electron microscopy and mass spectrometry to demonstrate that neutral and ionic dopants embedded in the droplets are efficiently backscattered in such events. High abundances of weakly bound He-tagged ions of both polarities indicate a gentle extraction mechanism of these ions from the droplets upon collision with a solid surface. This backscattering process is observed for dopant particles with masses up to 400 kilodaltons, indicating an unexpected mechanism that effectively lowers deposition rates of nanoparticles formed in helium droplets.
|
|
| 7. |
- Tiefenthaler, Lukas, et al.
(författare)
-
Isotope enrichment in neon clusters grown in helium nanodroplets
- 2020
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 153:16
-
Tidskriftsartikel (refereegranskat)abstract
- Neon cluster ions Ne-s(+) grown in pre-ionized, mass-to-charge selected helium nanodroplets (HNDs) reveal a strong enrichment of the heavy isotope Ne-22 that depends on cluster size s and the experimental conditions. For small sizes, the enrichment is much larger than previously reported for bare neon clusters grown in nozzle expansions and subsequently ionized. The enrichment is traced to the massive evaporation of neon atoms in a collision cell that is used to strip helium from the HNDs. We derive a relation between the enrichment of Ne-22 in the cluster ion and its corresponding depletion factor F in the vapor phase. The value thus found for F is in excellent agreement with a theoretical expression that relates isotopic fractionation in two-phase equilibria of atomic gases to the Debye temperature. Furthermore, the difference in zero-point energies between the two isotopes computed from F agrees reasonably well with theoretical studies of neon cluster ions that include nuclear quantum effects in the harmonic approximation. Another fitting parameter provides an estimate for the size s(i) of the precursor of the observed Ne-s(+). The value is in satisfactory agreement with the size estimated by modeling the growth of Ne-s(+) and with lower and upper limits deduced from other experimental data. On the other hand, neon clusters grown in neutral HNDs that are subsequently ionized by electron bombardment exhibit no statistically significant isotope enrichment at all. The finding suggests that the extent of ionization-induced dissociation of clusters embedded in HNDs is considerably smaller than that for bare clusters.
|
|
