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  • 1.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Goulart, Marcelo
    Kranabetter, Lorenz
    Kuhn, Martin
    Martini, Paul
    Rasul, Bilal
    Scheier, Paul
    Complexes of gold and imidazole formed in helium nanodroplets2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 11, p. 7739-7745Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Martini, Paul
    Laimer, Felix
    Goulart, Marcelo
    Calvo, Florent
    Scheier, Paul
    Spectroscopy of corannulene cations in helium nanodroplets2019In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 217, p. 276-289Article in journal (Refereed)
    Abstract [en]

    Helium tagging in action spectroscopy is an efficient method for measuring the absorption spectra of complex molecular ions with minimal perturbations to the gas phase spectra. We have used superfluid helium nanodroplets doped with corannulene to prepare cations of these molecules complexed with different numbers of He atoms. In total we identify 13 different absorption bands from corannulene cations between 5500 angstrom and 6000 angstrom. The He atoms cause a small, chemically induced redshift of the band positions of the corannulene ion. By studying this effect as a function of the number of solvating atoms we are able to identify the formation of solvation structures that are not visible in the mass spectrum. The solvation features detected using action spectroscopy agree very well with the results of atomistic modeling based on path-integral molecular dynamics simulations. By additionally doping our He droplets with D-2, we produce protonated corannulene ions. The absorption spectrum of these ions differs significantly from the case of the radical cations as the numerous narrow bands are replaced by a broad absorption feature that spans nearly 2000 angstrom in width.

  • 3. Kranabetter, Lorenz
    et al.
    Bersenkowitsch, Nina K.
    Martini, Paul
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Kuhn, Martin
    Laimer, Felix
    Schiller, Arne
    Beyer, Martin K.
    Ončák, Milan
    Scheier, Paul
    Considerable matrix shift in the electronic transitions of helium-solvated cesium dimer cation Cs2He+n2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 45, p. 25362-25368Article in journal (Refereed)
    Abstract [en]

    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.

  • 4. Laimer, Felix
    et al.
    Kranabetter, Lorenz
    Tiefenthaler, Lukas
    Albertini, Simon
    Zappa, Fabio
    Ellis, Andrew M.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Scheier, Paul
    Highly Charged Droplets of Superfluid Helium2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 16, article id 165301Article in journal (Refereed)
    Abstract [en]

    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.

  • 5. Lundberg, Linnea
    et al.
    Martini, Paul
    Goulart, Marcelo
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Bohme, Diethard K.
    Scheier, Paul
    Hydrogenated Gold Clusters from Helium Nanodroplets: Cluster Ionization and Affinities for Protons and Hydrogen Molecules2019In: Journal of the American Society for Mass Spectrometry, ISSN 1044-0305, E-ISSN 1879-1123, Vol. 30, no 10, p. 1906-1913Article in journal (Refereed)
    Abstract [en]

    We report the mass spectrometric detection of hydrogenated gold clusters ionized by electron transfer and proton transfer. The cations appear after the pickup of hydrogen molecules and gold atoms by helium nanodroplets (HNDs) near zero K and subsequent exposure to electron impact. We focus on the size distributions of the gold cluster cations and their hydrogen content, the electron energy dependence of the ion yield, patterns of hydrogenated gold cluster cation stability, and the presence of magic clusters. Ab initio molecular orbital calculations were performed to provide insight into ionization energies and proton affinities of gold clusters as well as into molecular hydrogen affinities of the ionized and protonated gold cluster cations.

  • 6. Martini, Paul
    et al.
    Kranabetter, Lorenz
    Goulart, Marcelo
    Rasul, Bilal
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Scheier, Paul
    Echt, Olof
    Atomic Gold Ions Clustered with Noble Gases: Helium, Neon, Argon, Krypton, and Xenon2019In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 123, no 44, p. 9505-9513Article in journal (Refereed)
    Abstract [en]

    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.

  • 7. Rastogi, Monisha
    et al.
    Leidlmair, Christian
    An der Lan, Lukas
    Ortiz de Zarate, Josu
    de Tudela, Ricardo Perez
    Bartolomei, Massimiliano
    Hernandez, Marta I.
    Campos-Martinez, Jose
    Gonzalez-Lezana, Tomas
    Hernandez-Rojas, Javier
    Breton, Jose
    Scheier, Paul
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Lithium ions solvated in helium2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 40, p. 25569-25576Article in journal (Refereed)
    Abstract [en]

    We report on a combined experimental and theoretical study of Li+ ions solvated by up to 50 He atoms. The experiments show clear enhanced abundances associated with HenLi+ clusters where n = 2, 6, 8, and 14. We find that classical methods, e.g. basin-hopping (BH), give results that qualitatively agree with quantum mechanical methods such as path integral Monte Carlo, diffusion Monte Carlo and quantum free energy, regarding both energies and the solvation structures that are formed. The theory identifies particularly stable structures for n = 4, 6 and 8 which line up with some of the most abundant features in the experiments.

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