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García-Alfonso E, Barranco M, Halberstadt N, Pi M. Time-resolved solvation of alkali ions in superfluid helium nanodroplets. J Chem Phys 2024; 160:164308. [PMID: 38651804 DOI: 10.1063/5.0205951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Accepted: 03/29/2024] [Indexed: 04/25/2024] Open
Abstract
The sinking of alkali cations in superfluid 4He nanodroplets is investigated theoretically using liquid 4He time-dependent density functional theory at zero temperature. The simulations illustrate the dynamics of the buildup of the first solvation shell around the ions. The number of helium atoms in this shell is found to linearly increase with time during the first stages of the dynamics. This points to a Poissonian capture process, as concluded in the work of Albrechtsen et al. on the primary steps of Na+ solvation in helium droplets [Albrechtsen et al., Nature 623, 319 (2023)]. The energy dissipation rate by helium atom ejection is found to be quite similar between all alkalis, the main difference being a larger energy dissipated per atom for the lighter alkalis at the beginning of the dynamics. In addition, the number of helium atoms in the first solvation shell is found to be lower at the end of the dynamics than at equilibrium for both Li+ and Na+, pointing to a kinetic rather than thermodynamical control of the snowball size for small and strongly attractive ions.
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Affiliation(s)
- Ernesto García-Alfonso
- Laboratoire Collisions, Agrégats, Réactivité (LCAR), Université de Toulouse, CNRS, 31062 Toulouse, France
| | - Manuel Barranco
- Departament FQA, Facultat de Física, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona, Spain
| | - Nadine Halberstadt
- Laboratoire Collisions, Agrégats, Réactivité (LCAR), Université de Toulouse, CNRS, 31062 Toulouse, France
| | - Martí Pi
- Departament FQA, Facultat de Física, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona, Spain
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2
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Ulmer A, Heilrath A, Senfftleben B, O'Connell-Lopez SMO, Kruse B, Seiffert L, Kolatzki K, Langbehn B, Hoffmann A, Baumann TM, Boll R, Chatterley AS, De Fanis A, Erk B, Erukala S, Feinberg AJ, Fennel T, Grychtol P, Hartmann R, Ilchen M, Izquierdo M, Krebs B, Kuster M, Mazza T, Montaño J, Noffz G, Rivas DE, Schlosser D, Seel F, Stapelfeldt H, Strüder L, Tiggesbäumker J, Yousef H, Zabel M, Ziołkowski P, Meyer M, Ovcharenko Y, Vilesov AF, Möller T, Rupp D, Tanyag RMP. Generation of Large Vortex-Free Superfluid Helium Nanodroplets. PHYSICAL REVIEW LETTERS 2023; 131:076002. [PMID: 37656857 DOI: 10.1103/physrevlett.131.076002] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Accepted: 06/22/2023] [Indexed: 09/03/2023]
Abstract
Superfluid helium nanodroplets are an ideal environment for the formation of metastable, self-organized dopant nanostructures. However, the presence of vortices often hinders their formation. Here, we demonstrate the generation of vortex-free helium nanodroplets and explore the size range in which they can be produced. From x-ray diffraction images of xenon-doped droplets, we identify that single compact structures, assigned to vortex-free aggregation, prevail up to 10^{8} atoms per droplet. This finding builds the basis for exploring the assembly of far-from-equilibrium nanostructures at low temperatures.
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Affiliation(s)
- Anatoli Ulmer
- Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
- Department of Physics, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - Andrea Heilrath
- Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
- Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2A, 12489 Berlin, Germany
| | - Björn Senfftleben
- Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2A, 12489 Berlin, Germany
- European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Sean M O O'Connell-Lopez
- Department of Chemistry, University of Southern California, 920 Bloom Walk, Los Angeles, California 90089, USA
| | - Björn Kruse
- Institute for Physics, Universität Rostock, Albert-Einstein-Straße 23, 18059 Rostock, Germany
| | - Lennart Seiffert
- Institute for Physics, Universität Rostock, Albert-Einstein-Straße 23, 18059 Rostock, Germany
| | - Katharina Kolatzki
- Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2A, 12489 Berlin, Germany
- Laboratory for Solid State Physics, Swiss Federal Institute of Technology in Zurich, John-von-Neumann-Weg 9, 8093 Zurich, Switzerland
| | - Bruno Langbehn
- Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
| | - Andreas Hoffmann
- Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2A, 12489 Berlin, Germany
| | | | - Rebecca Boll
- European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Adam S Chatterley
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
| | | | - Benjamin Erk
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | - Swetha Erukala
- Department of Chemistry, University of Southern California, 920 Bloom Walk, Los Angeles, California 90089, USA
| | - Alexandra J Feinberg
- Department of Chemistry, University of Southern California, 920 Bloom Walk, Los Angeles, California 90089, USA
| | - Thomas Fennel
- Institute for Physics, Universität Rostock, Albert-Einstein-Straße 23, 18059 Rostock, Germany
| | | | | | - Markus Ilchen
- European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
- Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany
| | | | - Bennet Krebs
- Institute for Physics, Universität Rostock, Albert-Einstein-Straße 23, 18059 Rostock, Germany
| | - Markus Kuster
- European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Tommaso Mazza
- European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | | | - Georg Noffz
- Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
| | | | | | - Fabian Seel
- Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
| | - Henrik Stapelfeldt
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
| | | | - Josef Tiggesbäumker
- Institute for Physics, Universität Rostock, Albert-Einstein-Straße 23, 18059 Rostock, Germany
- Department "Life, Light and Matter," Universität Rostock, Albert-Einstein-Straße 23, 18059 Rostock, Germany
| | - Hazem Yousef
- European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | - Michael Zabel
- Institute for Physics, Universität Rostock, Albert-Einstein-Straße 23, 18059 Rostock, Germany
| | | | - Michael Meyer
- European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany
| | | | - Andrey F Vilesov
- Department of Chemistry, University of Southern California, 920 Bloom Walk, Los Angeles, California 90089, USA
- Department of Physics and Astronomy, University of Southern California, 920 Bloom Walk, Los Angeles, California 90089, USA
| | - Thomas Möller
- Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
| | - Daniela Rupp
- Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2A, 12489 Berlin, Germany
- Laboratory for Solid State Physics, Swiss Federal Institute of Technology in Zurich, John-von-Neumann-Weg 9, 8093 Zurich, Switzerland
| | - Rico Mayro P Tanyag
- Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
- Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
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3
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Fischer J, Slenczka A. Formation of heterogeneous clusters in superfluid helium nanodroplets: phthalocyanine and water. Phys Chem Chem Phys 2023; 25:3287-3297. [PMID: 36629317 DOI: 10.1039/d2cp04514a] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Clusters consisting of a single phthalocyanine molecule and a single water molecule are investigated by means of electronic spectroscopy in superfluid helium droplets. A recent spectroscopic study of those clusters [J. Fischer, F. Schlaghaufer, E.-M. Lottner, A. Slenczka, L. Christiansen, H. Stapelfeldt, M. Karra, B. Friedrich, T. Mullan, M. Schütz and D. Usvyat, J. Phys. Chem. A, 2019, 123, 10057-10064] which all exhibit a water induced electronic shift to the red is now complemented by the corresponding clusters exhibiting a water induced shift to the blue. These clusters will be analyzed by means of fluorescence excitation spectra, dispersed emission spectra, and additional experimental observations made feasible by helium droplets as cryogenic reactor. Together with the blue shifted clusters a total number of at least 6 isomeric variants could be identified in helium droplets. This contrasts to a number of only three isomeric variants obtained from quantum chemical calculations [J. Fischer, F. Schlaghaufer, E.-M. Lottner, A. Slenczka, L. Christiansen, H. Stapelfeldt, M. Karra, B. Friedrich, T. Mullan, M. Schütz and D. Usvyat, J. Phys. Chem. A, 2019, 123, 10057-10064] disregarding the helium environment and to a single isomer identified in a molecular beam experiment [J. Menapace and E. Bernstein, J. Chem. Phys., 1987, 87, 6877-6889]. The discrepancy in the number of isomers provides evidence of a profound involvement of helium in clustering. Moreover, the discrepancies between the gas phase experiment and quantum chemical calculations similarly reveal the influence of the dynamics of cluster formation on the population of global and local minima that are accessible as isomeric variants.
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Affiliation(s)
- Johannes Fischer
- Institute for Physical and Theoretical Chemistry, University of Regensburg, Germany.
| | - Alkwin Slenczka
- Institute for Physical and Theoretical Chemistry, University of Regensburg, Germany.
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García-Alfonso E, Barranco M, Bonhommeau DA, Halberstadt N, Pi M, Calvo F. Clustering, collision, and relaxation dynamics in pure and doped helium nanoclusters: Density- vs particle-based approaches. J Chem Phys 2022; 157:014106. [DOI: 10.1063/5.0091942] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The clustering, collision, and relaxation dynamics of pristine and doped helium nanodroplets is theoretically investigated in cases of pickup and clustering of heliophilic argon, collision of heliophobic cesium atoms, and coalescence of two droplets brought into contact by their mutual long-range van der Waals interaction. Three approaches are used and compared with each other. The He time-dependent density functional theory method considers the droplet as a continuous medium and accounts for its superfluid character. The ring-polymer molecular dynamics method uses a path-integral description of nuclear motion and incorporates zero-point delocalization while bosonic exchange effects are ignored. Finally, the zero-point averaged dynamics approach is a mixed quantum–classical method in which quantum delocalization is described by attaching a frozen wavefunction to each He atom, equivalent to classical dynamics with effective interaction potentials. All three methods predict that the growth of argon clusters is significantly hindered by the helium host droplet due to the impeding shell structure around the dopants and kinematic effects freezing the growing cluster in metastable configurations. The effects of superfluidity are qualitatively manifested by different collision dynamics of the heliophilic atom at high velocities, as well as quadrupole oscillations that are not seen with particle-based methods, for droplets experiencing a collision with cesium atoms or merging with each other.
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Affiliation(s)
- Ernesto García-Alfonso
- Laboratoire Collisions, Agrégats, Réactivité (LCAR), Université de Toulouse, CNRS, 31062 Toulouse, France
| | - Manuel Barranco
- Laboratoire Collisions, Agrégats, Réactivité (LCAR), Université de Toulouse, CNRS, 31062 Toulouse, France
- Department FQA, Facultat de Física, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona, Spain
| | - David A. Bonhommeau
- Université de Reims Champagne Ardenne, CNRS, GSMA UMR 7331, 51100 Reims, France
| | - Nadine Halberstadt
- Laboratoire Collisions, Agrégats, Réactivité (LCAR), Université de Toulouse, CNRS, 31062 Toulouse, France
| | - Martí Pi
- Department FQA, Facultat de Física, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, Barcelona, Spain
| | - Florent Calvo
- Université Grenoble Alpes, CNRS, LIPHY, F38000 Grenoble, France
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5
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Feinberg AJ, Verma D, O’Connell-Lopez SM, Erukala S, Tanyag RMP, Pang W, Saladrigas CA, Toulson BW, Borgwardt M, Shivaram N, Lin MF, Al Haddad A, Jäger W, Bostedt C, Walter P, Gessner O, Vilesov AF. Aggregation of solutes in bosonic versus fermionic quantum fluids. SCIENCE ADVANCES 2021; 7:eabk2247. [PMID: 34890219 PMCID: PMC8664268 DOI: 10.1126/sciadv.abk2247] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 10/22/2021] [Indexed: 06/13/2023]
Abstract
Quantum fluid droplets made of helium-3 (3He) or helium-4 (4He) isotopes have long been considered as ideal cryogenic nanolabs, enabling unique ultracold chemistry and spectroscopy applications. The droplets were believed to provide a homogeneous environment in which dopant atoms and molecules could move and react almost as in free space but at temperatures close to absolute zero. Here, we report ultrafast x-ray diffraction experiments on xenon-doped 3He and 4He nanodroplets, demonstrating that the unavoidable rotational excitation of isolated droplets leads to highly anisotropic and inhomogeneous interactions between the host matrix and enclosed dopants. Superfluid 4He droplets are laced with quantum vortices that trap the embedded particles, leading to the formation of filament-shaped clusters. In comparison, dopants in 3He droplets gather in diffuse, ring-shaped structures along the equator. The shapes of droplets carrying filaments or rings are direct evidence that rotational excitation is the root cause for the inhomogeneous dopant distributions.
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Affiliation(s)
- Alexandra J. Feinberg
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Deepak Verma
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
- RA3, Intel Corporation, Ronler Acres, 2501 NE Century Blvd, Hillsboro, OR 97124, USA
| | - Sean M.O. O’Connell-Lopez
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
- Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149, USA
| | - Swetha Erukala
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Rico Mayro P. Tanyag
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
- Department of Chemistry, Aarhus University, 8000 Aarhus C, Denmark
| | - Weiwu Pang
- Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Catherine A. Saladrigas
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Benjamin W. Toulson
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Mario Borgwardt
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Niranjan Shivaram
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
- Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, USA
| | - Ming-Fu Lin
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
| | - Andre Al Haddad
- Laboratory for Femtochemistry (LSF), Paul Scherrer Institut, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland
| | - Wolfgang Jäger
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
| | - Christoph Bostedt
- Laboratory for Femtochemistry (LSF), Paul Scherrer Institut, Forschungsstrasse 111, 5232 Villigen-PSI, Switzerland
- LUXS Laboratory for Ultrafast X-ray Sciences, Institute for Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Peter Walter
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
| | - Oliver Gessner
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Andrey F. Vilesov
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
- Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA
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Blancafort-Jorquera M, González M. Vibrational energy relaxation of a diatomic molecule in a superfluid helium nanodroplet: influence of the nanodroplet size, interaction energy and energy gap. Phys Chem Chem Phys 2021; 23:25961-25973. [PMID: 34783338 DOI: 10.1039/d1cp03629g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The influence of the nanodroplet size, molecule-helium interaction potential energy and ν = 1 - ν = 0 vibrational energy gap on the vibrational energy relaxation (VER) of a diatomic molecule (X2) in a superfluid helium nanodroplet [HeND or (4He)N; finite quantum solvent at T = 0.37 K] has been studied using a hybrid quantum approach recently proposed by us and taking as a reference the VER results on the I2@(4He)100 doped nanodroplet (Vilà et al., Phys. Chem. Chem. Phys., 2018, 20, 118, which corresponds to the first theoretical study on the VER of molecules embedded in a HeND). This has allowed us to obtain a deeper insight into the vibrational relaxation dynamics. The nanodroplet size has a very small effect on the VER, as this process mainly depends on the interaction between the molecule and the nanodroplet first solvation shell. Regarding the interaction potential energy and the energy gap, both factors play an important and comparable role in the VER time properties (global relaxation time, lifetime and transition time). As the former becomes stronger the relaxation time properties decrease in a significant way (their inverse follows a linear dependence with respect to the ν = 1 - ν = 0 coupling term) and they also decrease in a significant manner when the energy gap diminishes (linear dependence on the ν = 1 - ν = 0 energy difference). We expect that this study will motivate further work on the vibrational relaxation process in HeNDs.
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Affiliation(s)
- Miquel Blancafort-Jorquera
- Departament de Ciència dels Materials i Química Física and IQTC, Universitat de Barcelona, Martí i Franquès, 1-11, 08028 Barcelona, Spain.
| | - Miguel González
- Departament de Ciència dels Materials i Química Física and IQTC, Universitat de Barcelona, Martí i Franquès, 1-11, 08028 Barcelona, Spain.
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A Path Integral Molecular Dynamics Simulation of a Harpoon-Type Redox Reaction in a Helium Nanodroplet. Molecules 2021; 26:molecules26195783. [PMID: 34641327 PMCID: PMC8510490 DOI: 10.3390/molecules26195783] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 09/14/2021] [Accepted: 09/21/2021] [Indexed: 11/17/2022] Open
Abstract
We present path integral molecular dynamics (PIMD) calculations of an electron transfer from a heliophobic Cs2 dimer in its (3Σu) state, located on the surface of a He droplet, to a heliophilic, fully immersed C60 molecule. Supported by electron ionization mass spectroscopy measurements (Renzler et al., J. Chem. Phys.2016, 145, 181101), this spatially quenched reaction was characterized as a harpoon-type or long-range electron transfer in a previous high-level ab initio study (de Lara-Castells et al., J. Phys. Chem. Lett.2017, 8, 4284). To go beyond the static approach, classical and quantum PIMD simulations are performed at 2 K, slightly below the critical temperature for helium superfluidity (2.172 K). Calculations are executed in the NVT ensemble as well as the NVE ensemble to provide insights into real-time dynamics. A droplet size of 2090 atoms is assumed to study the impact of spatial hindrance on reactivity. By changing the number of beads in the PIMD simulations, the impact of quantization can be studied in greater detail and without an implicit assumption of superfluidity. We find that the reaction probability increases with higher levels of quantization. Our findings confirm earlier, static predictions of a rotational motion of the Cs2 dimer upon reacting with the fullerene, involving a substantial displacement of helium. However, it also raises the new question of whether the interacting species are driven out-of-equilibrium after impurity uptake, since reactivity is strongly quenched if a full thermal equilibration is assumed. More generally, our work points towards a novel mechanism for long-range electron transfer through an interplay between nuclear quantum delocalization within the confining medium and delocalized electronic dispersion forces acting on the two reactants.
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Ernst WE, Hauser AW. Metal clusters synthesized in helium droplets: structure and dynamics from experiment and theory. Phys Chem Chem Phys 2020; 23:7553-7574. [PMID: 33057510 DOI: 10.1039/d0cp04349d] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Metal clusters have drawn continuous interest because of their high potential for the assembly of matter with special properties that may significantly differ from the corresponding bulk. Controlled combination of particular elements in one nanoparticle can increase the options for the creation of new materials for photonic, catalytic, or electronic applications. Superfluid helium droplets provide confinement and ultralow temperature, i.e. an ideal environment for the atom-by-atom aggregation of a new nanoparticle. This perspective presents a review of the current research progress on the synthesis of tailored metal and metal oxide clusters including core-shell designs, their characterization within the helium droplet beam, deposition on various solid substrates, and analysis via surface diagnostics. Special attention is given to the thermal properties of mixed metal clusters and questions about alloy formation on the nanoscale. Experimental results are accompanied by theoretical approaches employing computational chemistry, molecular dynamics simulations and He density functional theory.
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Affiliation(s)
- Wolfgang E Ernst
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria.
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9
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Halberstadt N, Bonhommeau DA. Fragmentation dynamics of Ar 4He 1000 upon electron impact ionization: Competition between ion ejection and trapping. J Chem Phys 2020; 152:234305. [PMID: 32571060 DOI: 10.1063/5.0009363] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The fragmentation upon electron impact ionization of Ar4He1000 is investigated by means of mixed quantum-classical dynamics simulations. The Ar4 + dopant dynamics is described by a surface hopping method coupled with a diatomics-in-molecules model to properly take into account the multiple Ar4 + electronic surfaces and possible transitions between them. Helium atoms are treated individually using zero-point averaged dynamics, a method based on the building of an effective He-He potential. Fast electronic relaxation is observed from less than 2 ps to ∼30 ps, depending on initial conditions. The main fragments observed are Ar2 +Heq and Ar3 +Heq (q ≤ 1000), with a strong contribution of the bare Ar2 + ion, and neither Ar+ nor Ar+Heq fragments are found. The smaller fragments (q ≤ 50) are found to mostly come from ion ejection, whereas larger fragments (q > 500) originate from long-term ion trapping. Although the structure of the trapped Ar2 + ions is the same as in the gas phase, trapped Ar3 + and Ar4 + are rather slightly bound Ar2 +⋯Ar and Ar2 +⋯Ar⋯Ar structures (i.e., an Ar2 + core with one or two argon atoms roaming within the droplet). These loose structures can undergo geminate recombination and release Ar3 +Heq or Ar4 +Heq (q ≤ 50) in the gas phase and/or induce strong helium droplet evaporation. Finally, the translational energy of the fragment center of mass was found to be suitable to provide a clear signature of the broad variety of processes at play in our simulations.
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Affiliation(s)
| | - David A Bonhommeau
- Université de Reims Champagne Ardenne, CNRS, GSMA UMR 7331, 51097 Reims, France
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García-Alfonso E, Coppens F, Barranco M, Pi M, Stienkemeier F, Halberstadt N. Alkali atoms attached to vortex-hosting helium nanodroplets. J Chem Phys 2020; 152:194109. [PMID: 33687233 DOI: 10.1063/5.0008923] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Light absorption or fluorescence excitation spectroscopy of alkali atoms attached to 4He droplets is investigated as a possible way for detecting the presence of vortices. To this end, we have calculated the equilibrium configuration and energetics of alkali atoms attached to a 4He1000 droplet hosting a vortex line using 4He density functional theory. We use them to study how the dipole absorption spectrum of the alkali atom is modified when the impurity is attached to a vortex line. Spectra are found to be blue-shifted (higher frequencies) and broadened compared to vortex-free droplets because the dimple in which the alkali atom sits at the intersection of the vortex line and the droplet surface is deeper. This effect is smaller for lighter alkali atoms and all the more so when using a quantum description since, in this case, they sit further away from the droplet surface on average due to their zero-point motion. Spectral modifications due to the presence of a vortex line are minor for np ← ns excitation and therefore insufficient for vortex detection. In the case of higher n'p ← ns or n's ← ns (n' > n) excitations, the shifts are larger as the excited state orbital is more extended and therefore more sensitive to changes in the surrounding helium density.
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Affiliation(s)
| | - Francois Coppens
- Université Toulouse 3 and CNRS, Laboratoire des Collisions, Agrégats et Réactivité, IRSAMC, 118 route de Narbonne, F-31062 Toulouse Cedex 09, France
| | - Manuel Barranco
- Université Toulouse 3 and CNRS, Laboratoire des Collisions, Agrégats et Réactivité, IRSAMC, 118 route de Narbonne, F-31062 Toulouse Cedex 09, France
| | - Martí Pi
- Departament FQA, Facultat de Física, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
| | | | - Nadine Halberstadt
- Université Toulouse 3 and CNRS, Laboratoire des Collisions, Agrégats et Réactivité, IRSAMC, 118 route de Narbonne, F-31062 Toulouse Cedex 09, France
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