1
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Fixot B, Louaas E, Bonhommeau DA. Collision of rare-gas atoms on helium nanodroplets: Theoretical evidence for an efficient coagulation of heavy rare-gas atoms. J Chem Phys 2024; 161:044307. [PMID: 39051833 DOI: 10.1063/5.0220027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2024] [Accepted: 07/08/2024] [Indexed: 07/27/2024] Open
Abstract
The coagulation of rare-gas atoms (RG = Ne, Ar, Kr, Xe, and Rn) in helium nanodroplets (HNDs) composed of 1000 atoms is investigated by zero-point averaged dynamics where a He-He pseudopotential is used to make the droplet liquid with proper energies. This method reproduces the qualitative abundances of embedded Arn+1 structures obtained by Time-Dependent Density Functional Theory and Ring Polymer Molecular Dynamics for Ar + ArnHe1000 collisions at realistic projectile speeds and impact parameters. More generally, coagulation is found to be much more efficient for heavy rare-gases (Xe and Rn) than for light ones (Ne and Ar), a behavior mainly attributed to a slower energy dissipation of the projectile in the HND. When coagulation does not occur, the projectile maintains a speed of 10-30 m s-1 within the HND, but its velocity vector is rarely oriented toward the dopant, and the projectile roams in a limited region of the droplet. The structure of embedded RGn+1 clusters does not systematically match their gas-phase global minimum structure, and more than 30% of RGn-RG unbound structures are due to one He atom located in between the projectile and a dopant atom.
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Affiliation(s)
- Brendan Fixot
- Université Paris-Saclay, Univ Evry, CY Cergy Paris Université, CNRS, LAMBE, Evry-Courcouronnes 91025, France
| | - Elsa Louaas
- Université Paris-Saclay, Univ Evry, CY Cergy Paris Université, CNRS, LAMBE, Evry-Courcouronnes 91025, France
| | - David A Bonhommeau
- Université Paris-Saclay, Univ Evry, CY Cergy Paris Université, CNRS, LAMBE, Evry-Courcouronnes 91025, France
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2
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De S, Abid AR, Asmussen JD, Ben Ltaief L, Sishodia K, Ulmer A, Pedersen HB, Krishnan SR, Mudrich M. Fragmentation of water clusters formed in helium nanodroplets by charge transfer and Penning ionization. J Chem Phys 2024; 160:094308. [PMID: 38445733 DOI: 10.1063/5.0194098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2023] [Accepted: 02/16/2024] [Indexed: 03/07/2024] Open
Abstract
Helium nanodroplets ("HNDs") are widely used for forming tailor-made clusters and molecular complexes in a cold, transparent, and weakly interacting matrix. The characterization of embedded species by mass spectrometry is often complicated by the fragmentation and trapping of ions in the HNDs. Here, we systematically study fragment ion mass spectra of HND-aggregated water and oxygen clusters following their ionization by charge transfer ionization ("CTI") and Penning ionization ("PEI"). While the efficiency of PEI of embedded clusters is lower than for CTI by about factor 10, both the mean sizes of detected water clusters and the relative yields of unprotonated cluster ions are significantly larger, making PEI a "soft ionization" scheme. However, the tendency of ions to remain bound to HNDs leads to a reduced detection efficiency for large HNDs containing >104 helium atoms. These results are instrumental in determining optimal conditions for mass spectrometry and photoionization spectroscopy of molecular complexes and clusters aggregated in HNDs.
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Affiliation(s)
- S De
- Quantum Center of Excellence for Diamond and Emergent Materials and Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
| | - A R Abid
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - J D Asmussen
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - L Ben Ltaief
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - K Sishodia
- Quantum Center of Excellence for Diamond and Emergent Materials and Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
| | - A Ulmer
- Department of Physics, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
| | - H B Pedersen
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - S R Krishnan
- Quantum Center of Excellence for Diamond and Emergent Materials and Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
| | - M Mudrich
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
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3
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Asmussen JD, Abid AR, Sundaralingam A, Bastian B, Sishodia K, De S, Ben Ltaief L, Krishnan S, Pedersen HB, Mudrich M. Secondary ionization of pyrimidine nucleobases and their microhydrated derivatives in helium nanodroplets. Phys Chem Chem Phys 2023; 25:24819-24828. [PMID: 37671772 DOI: 10.1039/d3cp02879h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/07/2023]
Abstract
Radiation damage in biological systems by ionizing radiation is predominantly caused by secondary processes such as charge and energy transfer leading to the breaking of bonds in DNA. Here, we study the fragmentation of cytosine (Cyt) and thymine (Thy) molecules, clusters and microhydrated derivatives induced by direct and indirect ionization initiated by extreme-ultraviolet (XUV) irradiation. Photofragmentation mass spectra and photoelectron spectra of free Cyt and Thy molecules are compared with mass and electron spectra of Cyt/Thy clusters and microhydrated Cyt/Thy molecules formed by aggregation in superfluid helium (He) nanodroplets. Penning ionization after resonant excitation of the He droplets is generally found to cause less fragmentation compared to direct photoionization and charge-transfer ionization after photoionization of the He droplets. When Cyt/Thy molecules and oligomers are complexed with water molecules, their fragmentation is efficiently suppressed. However, a similar suppression of fragmentation is observed when homogeneous Cyt/Thy clusters are formed in He nanodroplets, indicating a general trend. Penning ionization electron spectra (PIES) of Cyt/Thy are broad and nearly featureless but PIES of their microhydrated derivatives point at a sequential ionization process ending in unfragmented microsolvated Cyt/Thy cations.
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Affiliation(s)
- Jakob D Asmussen
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
| | - Abdul R Abid
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
| | | | - Björn Bastian
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
| | - Keshav Sishodia
- Quantum Center of Excellence for Diamond and Emergent Materials and Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
| | - Subhendu De
- Quantum Center of Excellence for Diamond and Emergent Materials and Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
| | - Ltaief Ben Ltaief
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
| | - Sivarama Krishnan
- Quantum Center of Excellence for Diamond and Emergent Materials and Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India
| | - Henrik B Pedersen
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
| | - Marcel Mudrich
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark.
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4
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Zunzunegui-Bru E, Gruber E, Lázaro T, Bartolomei M, Hernández MI, Campos-Martínez J, González-Lezana T, Bergmeister S, Zappa F, Scheier P, Pérez de Tudela R, Hernández-Rojas J, Bretón J. Observation of Multiple Ordered Solvation Shells in Doped Helium Droplets: The Case of He NCa 2. J Phys Chem Lett 2023; 14:3126-3131. [PMID: 36952614 PMCID: PMC10084467 DOI: 10.1021/acs.jpclett.3c00224] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
In this Letter, we report the experimental detection of likely the largest ordered structure of helium atoms surrounding a monatomic impurity observed to date using a recently developed technique. The mass spectrometry investigation of HeNCa2+ clusters, formed in multiply charged helium nanodroplets, reveals magic numbers at N = 12, 32, 44, and 74. Classical optimization and path integral Monte Carlo calculations suggest the existence of up to four shells surrounding the calcium dication which are closed with well-ordered Mozartkugel-like structures: He12Ca2+ with an icosahedron, the second at He32Ca2+ with a dodecahedron, the third at He44Ca2+ with a larger icosahedron, and finally for He74Ca2+, we find that the outermost He atoms form an icosidodecahedron which contains the other inner shells. We analyze the reasons for the formation of such ordered shells in order to guide the selection of possible candidates to exhibit a similar behavior.
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Affiliation(s)
- Eva Zunzunegui-Bru
- Instituto de Física Fundamental, IFF-CSIC, Serrano 123, Madrid 28006, Spain
| | - Elisabeth Gruber
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, Innsbruck 6020, Austria
| | - Teresa Lázaro
- Instituto de Física Fundamental, IFF-CSIC, Serrano 123, Madrid 28006, Spain
| | | | - Marta I Hernández
- Instituto de Física Fundamental, IFF-CSIC, Serrano 123, Madrid 28006, Spain
| | | | | | - Stefan Bergmeister
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, Innsbruck 6020, Austria
| | - Fabio Zappa
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, Innsbruck 6020, Austria
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, Innsbruck 6020, Austria
| | | | - Javier Hernández-Rojas
- Departamento de Física and IUdEA, Universidad de La Laguna, La Laguna, 38205, Tenerife, Spain
| | - José Bretón
- Departamento de Física and IUdEA, Universidad de La Laguna, La Laguna, 38205, Tenerife, Spain
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5
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Albertini S, Gruber E, Zappa F, Krasnokutski S, Laimer F, Scheier P. Chemistry and physics of dopants embedded in helium droplets. MASS SPECTROMETRY REVIEWS 2022; 41:529-567. [PMID: 33993543 DOI: 10.1002/mas.21699] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 04/20/2021] [Accepted: 04/20/2021] [Indexed: 05/18/2023]
Abstract
Helium droplets represent a cold inert matrix, free of walls with outstanding properties to grow complexes and clusters at conditions that are perfect to simulate cold and dense regions of the interstellar medium. At sub-Kelvin temperatures, barrierless reactions triggered by radicals or ions have been observed and studied by optical spectroscopy and mass spectrometry. The present review summarizes developments of experimental techniques and methods and recent results they enabled.
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Affiliation(s)
- Simon Albertini
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Elisabeth Gruber
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Fabio Zappa
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Serge Krasnokutski
- Laboratory Astrophysics Group of the MPI for Astronomy, University of Jena, Jena, Germany
| | - Felix Laimer
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
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6
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Bonhommeau DA. Zero-point averaged dynamics of Arn+He1000: Dopant-size influence on potential-energy surfaces, mass spectra and fragmentation patterns. Chem Phys 2021. [DOI: 10.1016/j.chemphys.2021.111307] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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7
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González-Lezana T, Echt O, Gatchell M, Bartolomei M, Campos-Martínez J, Scheier P. Solvation of ions in helium. INT REV PHYS CHEM 2020. [DOI: 10.1080/0144235x.2020.1794585] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- Tomás González-Lezana
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas IFF-CSIC, Madrid, Spain
| | - Olof Echt
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
- Department of Physics, University of New Hampshire, Durham, NH, USA
| | - Michael Gatchell
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
- Department of Physics, Stockholm University, Stockholm, Sweden
| | - Massimiliano Bartolomei
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas IFF-CSIC, Madrid, Spain
| | - José Campos-Martínez
- Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas IFF-CSIC, Madrid, Spain
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
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8
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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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9
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Abstract
We report suppression of multiphoton ionization (MPI) of aniline doped large superfluid helium droplets containing over 5 × 106 atoms. In contrast, surface-bound sodium atoms and dimers are readily desorbed and ionized. Adequacy of the experimental conditions is also confirmed from ejection of embedded aniline cations from smaller droplets containing multiple cations, and MPI of gaseous aniline. The photoelectrons have a mean-free-path of less than 1 nm and a thermalization distance of 10 nm. In a droplet with a diameter of over 70 nm, effective charge recombination within the droplet is expected.
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10
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Ionization dynamics of Ne-doped helium clusters at low temperature: Ring-polymer molecular dynamics simulations including electronically nonadiabatic transitions. COMPUT THEOR CHEM 2019. [DOI: 10.1016/j.comptc.2019.112537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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11
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Pérez de Tudela R, Martini P, Goulart M, Scheier P, Pirani F, Hernández-Rojas J, Bretón J, Ortiz de Zárate J, Bartolomei M, González-Lezana T, Hernández MI, Campos-Martínez J, Villarreal P. A combined experimental and theoretical investigation of Cs + ions solvated in He N clusters. J Chem Phys 2019; 150:154304. [PMID: 31005067 DOI: 10.1063/1.5092566] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Solvation of Cs+ ions inside helium droplets has been investigated both experimentally and theoretically. On the one hand, mass spectra of doped helium clusters ionized with a crossed electron beam, HeNCs+, have been recorded for sizes up to N = 60. The analysis of the ratio between the observed peaks for each size N reveals evidences of the closure of the first solvation shell when 17 He atoms surround the alkali ion. On the other hand, we have obtained energies and geometrical structures of the title clusters by means of basin-hopping, diffusion Monte Carlo (DMC), and path integral Monte Carlo (PIMC) methods. The analytical He-Cs+ interaction potential employed in our calculations is represented by the improved Lennard-Jones expression optimized on high level ab initio energies. The weakness of the existing interaction between helium and Cs+ in comparison with some other alkali ions such as Li+ is found to play a crucial role. Our theoretical findings confirm that the first solvation layer is completed at N = 17 and both evaporation and second difference energies obtained with the PIMC calculation seem to reproduce a feature observed at N = 12 for the experimental ion abundance. The analysis of the DMC probability distributions reveals the important contribution from the icosahedral structure to the overall configuration for He12Cs+.
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Affiliation(s)
| | - Paul Martini
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
| | - Marcelo Goulart
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria
| | - Fernando Pirani
- Dipartimento di Chimica, Biologia e Biotecnologie, Universitá di Perugia, 06123 Perugia, Italy
| | - Javier Hernández-Rojas
- Departamento de Física and IUdEA, Universidad de La Laguna, La Laguna, 38205 Tenerife, Spain
| | - José Bretón
- Departamento de Física and IUdEA, Universidad de La Laguna, La Laguna, 38205 Tenerife, Spain
| | | | | | | | - Marta I Hernández
- Instituto de Física Fundamental, IFF-CSIC, Serrano 123, 28006 Madrid, Spain
| | | | - Pablo Villarreal
- Instituto de Física Fundamental, IFF-CSIC, Serrano 123, 28006 Madrid, Spain
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12
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Shcherbinin M, LaForge AC, Hanif M, Richter R, Mudrich M. Penning Ionization of Acene Molecules by Helium Nanodroplets. J Phys Chem A 2018; 122:1855-1860. [DOI: 10.1021/acs.jpca.7b12506] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. Shcherbinin
- Department
of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - A. C. LaForge
- Physikalisches
Institut, Universität Freiburg, 79104 Freiburg, Germany
| | - M. Hanif
- Department
of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
| | - R. Richter
- Elettra Sincrotrone, 34149 Basovizza, Trieste, Italy
| | - M. Mudrich
- Department
of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
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13
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Chen L, Zhang J, Freund WM, Kong W. Effect of kinetic energy on the doping efficiency of cesium cations into superfluid helium droplets. J Chem Phys 2015; 143:044310. [PMID: 26233132 PMCID: PMC4522010 DOI: 10.1063/1.4927471] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 07/15/2015] [Indexed: 11/14/2022] Open
Abstract
We present an experimental investigation of the effect of kinetic energy on the ion doping efficiency of superfluid helium droplets using cesium cations from a thermionic emission source. The kinetic energy of Cs(+) is controlled by the bias voltage of a collection grid collinearly arranged with the droplet beam. Efficient doping from ions with kinetic energies from 20 eV up to 480 V has been observed in different sized helium droplets. The relative ion doping efficiency is determined by both the kinetic energy of the ions and the average size of the droplet beam. At a fixed source temperature, the number of doped droplets increases with increasing grid voltage, while the relative ion doping efficiency decreases. This result implies that not all ions are captured upon encountering with a sufficiently large droplet, a deviation from the near unity doping efficiency for closed shell neutral molecules. We propose that this drop in ion doping efficiency with kinetic energy is related to the limited deceleration rate inside a helium droplet. When the source temperature changes from 14 K to 17 K, the relative ion doping efficiency decreases rapidly, perhaps due to the lack of viable sized droplets. The size distribution of the Cs(+)-doped droplet beam can be measured by deflection and by energy filtering. The observed doped droplet size is about 5 × 10(6) helium atoms when the source temperature is between 14 K and 17 K.
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Affiliation(s)
- Lei Chen
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - Jie Zhang
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - William M Freund
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - Wei Kong
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
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14
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Ziemkiewicz MP, Neumark DM, Gessner O. Ultrafast electronic dynamics in helium nanodroplets. INT REV PHYS CHEM 2015. [DOI: 10.1080/0144235x.2015.1051353] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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15
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Renzler M, Daxner M, Weinberger N, Denifl S, Scheier P, Echt O. On subthreshold ionization of helium droplets, ejection of He(+), and the role of anions. Phys Chem Chem Phys 2015; 16:22466-70. [PMID: 25230760 DOI: 10.1039/c4cp03236e] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The mechanism of ionization of helium droplets has been investigated in numerous reports but one observation has not found a satisfactory explanation: How are He(+) ions formed and ejected from undoped droplets at electron energies below the ionization threshold of the free atom? Does this path exist at all? A measurement of the ion yields of He(+) and He2(+) as a function of electron energy, electron emission current, and droplet size reveals that metastable He*(-) anions play a crucial role in the formation of free He(+) at subthreshold energies. The proposed model is testable.
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Affiliation(s)
- Michael Renzler
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria.
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16
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Calvo F. Coating Polycyclic Aromatic Hydrocarbon Cations with Helium Clusters: Snowballs and Slush. J Phys Chem A 2014; 119:5959-70. [DOI: 10.1021/jp510799h] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Florent Calvo
- University of Grenoble Alpes, LIPHY, F-38000 Grenoble, France and
- CNRS, LIPHY, F-38000 Grenoble, France
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17
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Bartl P, Leidlmair C, Denifl S, Scheier P, Echt O. On the size and structure of helium snowballs formed around charged atoms and clusters of noble gases. J Phys Chem A 2014; 118:8050-9. [PMID: 24128371 PMCID: PMC4166691 DOI: 10.1021/jp406540p] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2013] [Revised: 09/04/2013] [Indexed: 11/30/2022]
Abstract
Helium nanodroplets doped with argon, krypton, or xenon are ionized by electrons and analyzed in a mass spectrometer. HenNgx(+) ions containing up to seven noble gas (Ng) atoms and dozens of helium atoms are identified; the high resolution of the mass spectrometer combined with advanced data analysis make it possible to unscramble contributions from isotopologues that have the same nominal mass but different numbers of helium or Ng atoms, such as the magic He20(84)Kr2(+) and the isobaric, nonmagic He41(84)Kr(+). Anomalies in these ion abundances reveal particularly stable ions; several intriguing patterns emerge. Perhaps most astounding are the results for HenAr(+), which show evidence for three distinct, solid-like solvation shells containing 12, 20, and 12 helium atoms. This observation runs counter to the common notion that only the first solvation shell is solid-like but agrees with calculations by Galli et al. for HenNa(+) [J. Phys. Chem. A 2011, 115, 7300] that reveal three shells of icosahedral symmetry. HenArx(+) (2 ≤ x ≤ 7) ions appear to be especially stable if they contain a total of n + x = 19 atoms. A sequence of anomalies in the abundance distribution of HenKrx(+) suggests that rings of six helium atoms are inserted into the solvation shell each time a krypton atom is added to the ionic core, from Kr(+) to Kr3(+). Previously reported strong anomalies at He12Kr2(+) and He12Kr3(+) [Kim , J. H.; et al. J. Chem. Phys. 2006, 124, 214301] are attributed to a contamination. Only minor local anomalies appear in the distributions of HenXex(+) (x ≤ 3). The distributions of HenKr(+) and HenXe(+) show strikingly similar, broad features that are absent from the distribution of HenAr(+); differences are tentatively ascribed to the very different fragmentation dynamics of these ions.
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Affiliation(s)
- Peter Bartl
- Institut für Ionenphysik und Angewandte Physik, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Christian Leidlmair
- Institut für Ionenphysik und Angewandte Physik, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Stephan Denifl
- Institut für Ionenphysik und Angewandte Physik, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Olof Echt
- Institut für Ionenphysik und Angewandte Physik, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
- Department of Physics, University of New Hampshire, Durham, New Hampshire 03824, United States
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18
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Buchta D, Krishnan SR, Brauer NB, Drabbels M, O’Keeffe P, Devetta M, Di Fraia M, Callegari C, Richter R, Coreno M, Prince KC, Stienkemeier F, Ullrich J, Moshammer R, Mudrich M. Extreme ultraviolet ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra. J Chem Phys 2013; 139:084301. [DOI: 10.1063/1.4818531] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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20
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Kaiser A, Leidlmair C, Bartl P, Zöttl S, Denifl S, Mauracher A, Probst M, Scheier P, Echt O. Adsorption of hydrogen on neutral and charged fullerene: experiment and theory. J Chem Phys 2013; 138:074311. [PMID: 23445013 DOI: 10.1063/1.4790403] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Helium droplets are doped with fullerenes (either C60 or C70) and hydrogen (H2 or D2) and investigated by high-resolution mass spectrometry. In addition to pure helium and hydrogen cluster ions, hydrogen-fullerene complexes are observed upon electron ionization. The composition of the main ion series is (H2)(n)HC(m)(+) where m = 60 or 70. Another series of even-numbered ions, (H2)(n)C(m)(+), is slightly weaker in stark contrast to pure hydrogen cluster ions for which the even-numbered series (H2)(n)(+) is barely detectable. The ion series (H2)(n)HC(m)(+) and (H2)(n)C(m)(+) exhibit abrupt drops in ion abundance at n = 32 for C60 and 37 for C70, indicating formation of an energetically favorable commensurate phase, with each face of the fullerene ion being covered by one adsorbate molecule. However, the first solvation layer is not complete until a total of 49 H2 are adsorbed on C60(+); the corresponding value for C70(+) is 51. Surprisingly, these values do not exhibit a hydrogen-deuterium isotope effect even though the isotope effect for H2/D2 adsorbates on graphite exceeds 6%. We also observe doubly charged fullerene-deuterium clusters; they, too, exhibit abrupt drops in ion abundance at n = 32 and 37 for C60 and C70, respectively. The findings imply that the charge is localized on the fullerene, stabilizing the system against charge separation. Density functional calculations for C60-hydrogen complexes with up to five hydrogen atoms provide insight into the experimental findings and the structure of the ions. The binding energy of physisorbed H2 is 57 meV for H2C60(+) and (H2)2C60(+), and slightly above 70 meV for H2HC60(+) and (H2)2HC60(+). The lone hydrogen in the odd-numbered complexes is covalently bound atop a carbon atom but a large barrier of 1.69 eV impedes chemisorption of the H2 molecules. Calculations for neutral and doubly charged complexes are presented as well.
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Affiliation(s)
- A Kaiser
- Institut für Ionenphysik und Angewandte Physik, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
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21
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Bartl P, Denifl S, Scheier P, Echt O. On the stability of cationic complexes of neon with helium--solving an experimental discrepancy. Phys Chem Chem Phys 2013; 15:16599-604. [PMID: 23958826 DOI: 10.1039/c3cp52550c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Helium nanodroplets are doped with neon and ionized by electrons. The size-dependence of the ion abundance of HenNex(+), identified in high-resolution mass spectra, is deduced for complexes containing up to seven neon atoms and dozens of helium atoms. Particularly stable ions are inferred from anomalies in the abundance distributions. Two pronounced anomalies at n = 11 and 13 in the HenNe(+) series confirm drift-tube data reported by Kojima et al. [T. M. Kojima et al., Z. Phys. D, 1992, 22, 645]. The discrepancy with previously published spectra of neon-doped helium droplets, which did not reveal any abundance anomalies [T. Ruchti et al., J. Chem. Phys., 1998, 109, 10679-10687; C. A. Brindle et al., J. Chem. Phys., 2005, 123, 064312], is most likely due to limited mass resolution, which precluded unambiguous analysis of contributions from different ions with identical nominal mass. However, calculated dissociation energies of HenNe(+) reported so far do not correlate with the present data, possibly because of challenges in correctly treating the linear, asymmetric [He-Ne-He](+) ionic core in HenNe(+). Anomalies identified in the distributions of HenNex(+) for x > 1, including prominent ones at He12Ne2(+) and He14Ne2(+), may help to better understand solvation of Ne(+) and Nex(+) in helium.
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Affiliation(s)
- Peter Bartl
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria.
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22
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Buchta D, Krishnan SR, Brauer NB, Drabbels M, O’Keeffe P, Devetta M, Di Fraia M, Callegari C, Richter R, Coreno M, Prince KC, Stienkemeier F, Moshammer R, Mudrich M. Charge Transfer and Penning Ionization of Dopants in or on Helium Nanodroplets Exposed to EUV Radiation. J Phys Chem A 2013; 117:4394-403. [DOI: 10.1021/jp401424w] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Dominic Buchta
- Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany
| | | | - Nils B. Brauer
- Laboratoire de Chimie Physique Moléculaire, Swiss Federal Institute of Technology Lausanne (EPFL), 1015
Lausanne, Switzerland
| | - Marcel Drabbels
- Laboratoire de Chimie Physique Moléculaire, Swiss Federal Institute of Technology Lausanne (EPFL), 1015
Lausanne, Switzerland
| | - Patrick O’Keeffe
- CNR Istituto di Metodologie Inorganiche e dei Plasmi, CP10, 00016 Monterotondo Scalo, Italy
| | - Michele Devetta
- CIMAINA and Dipartimento di Fisica, Università di Milano, 20133 Milano, Italy
| | - Michele Di Fraia
- Department of Physics, University of Trieste, 34128 Trieste, Italy
| | - Carlo Callegari
- Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy
| | - Robert Richter
- Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy
| | - Marcello Coreno
- CNR Istituto di Metodologie Inorganiche e dei Plasmi, CP10, 00016 Monterotondo Scalo, Italy
| | - Kevin C. Prince
- Elettra-Sincrotrone Trieste, 34149 Basovizza, Trieste, Italy
| | | | | | - Marcel Mudrich
- Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany
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23
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Bartl P, Leidlmair C, Denifl S, Scheier P, Echt O. Cationic complexes of hydrogen with helium. Chemphyschem 2013; 14:227-32. [PMID: 23090688 PMCID: PMC3555426 DOI: 10.1002/cphc.201200664] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Indexed: 11/08/2022]
Abstract
High-resolution mass spectra of helium nanodroplets doped with hydrogen or deuterium reveal that copious amounts of helium can be bound to H(+), H(2)(+), H(3)(+), and larger hydrogen-cluster ions. All conceivable He(n)H(x)(+) stoichiometries are identified if their mass is below the limit of ≈120 u set by the resolution of the spectrometer. Anomalies in the ion yields of He(n)H(x)(+) for x=1, 2, or 3, and n≤30 reveal particularly stable cluster ions. Our results for He(n)H(1)(+) are consistent with conclusions drawn from previous experimental and theoretical studies which were limited to smaller cluster ions. The He(n)H(3)(+) series exhibits a pronounced anomaly at n=12 which was outside the reliable range of earlier experiments. Contrary to findings reported for other diatomic dopant molecules, the monomer ion (i.e. H(2)(+)) retains helium with much greater efficiency than hydrogen-cluster ions.
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Affiliation(s)
- Peter Bartl
- Institut für Ionenphysik und Angewandte Physik, Universität InnsbruckTechnikerstraße 25, A-6020 Innsbruck (Austria)
| | - Christian Leidlmair
- Institut für Ionenphysik und Angewandte Physik, Universität InnsbruckTechnikerstraße 25, A-6020 Innsbruck (Austria)
| | - Stephan Denifl
- Institut für Ionenphysik und Angewandte Physik, Universität InnsbruckTechnikerstraße 25, A-6020 Innsbruck (Austria)
| | - Paul Scheier
- Institut für Ionenphysik und Angewandte Physik, Universität InnsbruckTechnikerstraße 25, A-6020 Innsbruck (Austria)
| | - Olof Echt
- Institut für Ionenphysik und Angewandte Physik, Universität InnsbruckTechnikerstraße 25, A-6020 Innsbruck (Austria)
- Department of Physics, University of New HampshireDurham, NH 03824 (USA)
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24
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An der Lan L, Bartl P, Leidlmair C, Jochum R, Denifl S, Echt O, Scheier P. Solvation of Na+, K+, and their dimers in helium. Chemistry 2012; 18:4411-8. [PMID: 22374575 PMCID: PMC3350777 DOI: 10.1002/chem.201103432] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Indexed: 11/10/2022]
Abstract
Helium atoms bind strongly to alkali cations which, when embedded in liquid helium, form so-called snowballs. Calculations suggest that helium atoms in the first solvation layer of these snowballs form rigid structures and that their number (n) is well defined, especially for the lighter alkalis. However, experiments have so far failed to accurately determine values of n. We present high-resolution mass spectra of Na+Hen, K+Hen, Na2+Hen and K2+Hen, formed by electron ionization of doped helium droplets; the data allow for a critical comparison with several theoretical studies. For sodium and potassium monomers the spectra indicate that the value of n is slightly smaller than calculated. Na2+Hen displays two distinct anomalies at n=2 and n=6, in agreement with theory; dissociation energies derived from experiment closely track theoretical values. K2+Hen distributions are fairly featureless, which also agrees with predictions.
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Affiliation(s)
- Lukas An der Lan
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
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25
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Golan A, Ahmed M. Ionization of Water Clusters Mediated by Exciton Energy Transfer from Argon Clusters. J Phys Chem Lett 2012; 3:458-462. [PMID: 26286046 DOI: 10.1021/jz2016654] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The exciton energy deposited in an argon cluster (Arn, ⟨n = 20⟩) using VUV radiation is transferred to softly ionize doped water clusters ((H2O)n, n = 1-9), leading to the formation of nonfragmented clusters. Following the initial excitation, electronic energy is channeled to ionize the doped water cluster while evaporating the Ar shell, allowing identification of fragmented and complete water cluster ions. Examination of the photoionization efficiency curve shows that cluster evaporation from excitons located above 12.6 eV is not enough to cool the energized water cluster ion and leads to their dissociation to (H2O)n-2H(+) (protonated) clusters.
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Affiliation(s)
- Amir Golan
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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26
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Zúniga J, Bastida A, Requena A, Halberstadt N, Beswick JA, Janda KC. Vibrational Bound States of the He2Ne+ Cation. J Phys Chem A 2009; 113:14896-903. [DOI: 10.1021/jp905043t] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- José Zúniga
- Departamento de Química Física, Universidad de Murcia, 3010 Murcia, Spain, Laboratoire Collisions, Agrégats, Réactivité, IRSAMC, Université de Toulouse, UPS, and CNRS, UMR5589, F-31062 Toulouse, France, and Department of Chemistry and Institute of Surface and Interface Science, University of California at Irvine, Irvine, California 92697-2025
| | - Adolfo Bastida
- Departamento de Química Física, Universidad de Murcia, 3010 Murcia, Spain, Laboratoire Collisions, Agrégats, Réactivité, IRSAMC, Université de Toulouse, UPS, and CNRS, UMR5589, F-31062 Toulouse, France, and Department of Chemistry and Institute of Surface and Interface Science, University of California at Irvine, Irvine, California 92697-2025
| | - Alberto Requena
- Departamento de Química Física, Universidad de Murcia, 3010 Murcia, Spain, Laboratoire Collisions, Agrégats, Réactivité, IRSAMC, Université de Toulouse, UPS, and CNRS, UMR5589, F-31062 Toulouse, France, and Department of Chemistry and Institute of Surface and Interface Science, University of California at Irvine, Irvine, California 92697-2025
| | - Nadine Halberstadt
- Departamento de Química Física, Universidad de Murcia, 3010 Murcia, Spain, Laboratoire Collisions, Agrégats, Réactivité, IRSAMC, Université de Toulouse, UPS, and CNRS, UMR5589, F-31062 Toulouse, France, and Department of Chemistry and Institute of Surface and Interface Science, University of California at Irvine, Irvine, California 92697-2025
| | - J. Alberto Beswick
- Departamento de Química Física, Universidad de Murcia, 3010 Murcia, Spain, Laboratoire Collisions, Agrégats, Réactivité, IRSAMC, Université de Toulouse, UPS, and CNRS, UMR5589, F-31062 Toulouse, France, and Department of Chemistry and Institute of Surface and Interface Science, University of California at Irvine, Irvine, California 92697-2025
| | - Kenneth C. Janda
- Departamento de Química Física, Universidad de Murcia, 3010 Murcia, Spain, Laboratoire Collisions, Agrégats, Réactivité, IRSAMC, Université de Toulouse, UPS, and CNRS, UMR5589, F-31062 Toulouse, France, and Department of Chemistry and Institute of Surface and Interface Science, University of California at Irvine, Irvine, California 92697-2025
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27
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da Silva FF, Bartl P, Denifl S, Echt O, Märk TD, Scheier P. Argon clusters embedded in helium nanodroplets. Phys Chem Chem Phys 2009; 11:9791-7. [PMID: 19851558 DOI: 10.1039/b913175b] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Electron impact ionization of argon clusters embedded in helium droplets is investigated. Superior mass resolution makes it possible to distinguish between nominally isobaric cluster ions. An abundance maximum for ArHe(12)(+) is unambiguously confirmed; the spectra also prove the formation of Ar(2)He(n)(+) complexes that had been claimed to fragment into pure Ar(2)(+). Distributions of larger argon cluster ions containing up to 60 atoms closely resemble distributions observed upon electron impact or photoionization of bare argon clusters; caging and evaporative cooling provided by the helium matrix do not suffice to quench fragmentation of the nascent argon cluster ions. Intriguing abundance anomalies are observed in distributions of argon cluster ions that contain water, nitrogen or oxygen impurities. The strong abundance of Ar(55)H(2)O(+), Ar(54)O(2)(+) and Ar(54)N(2)(+) contrasts with the virtual absence of slightly larger cluster ions containing the corresponding impurities. The features are probably related to enhanced cluster ion stability upon closure of the second icosahedral shell but the difference in magic numbers (54 versus 55) and the well-known reactivity of charged argon-nitrogen complexes suggest structural differences.
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Affiliation(s)
- Filipe Ferreira da Silva
- Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universität, Technikerstr. 25, A-6020 Innsbruck, Austria
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28
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Marinetti F, Bodo E, Gianturco FA, Yurtsever E. Energetics and structures of charged helium clusters: comparing stabilities of dimer and trimer cationic cores. Chemphyschem 2009; 9:2618-24. [PMID: 19012312 DOI: 10.1002/cphc.200800457] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We present accurate ab initio calculations of the most stable structures of He(n)(+) clusters in order to determine the more likely ionic core arrangements existing after reaching structural equilibrium of the clusters. Two potential energy surfaces are presented: one for the He(2)(+) and the other with the He(3)(+) linear ion, both interacting with one He atom. The two computed potentials are in turn employed within a classical structure optimization where the overall interaction forces are obtained within the sum-of-potentials approximation described in the main text. Because of the presence of many-body effects within the ionic core, we find that the arrangements with He(3)(+) as a core turn out to be energetically preferred, leading to the formation of He(3)(+)(He)(n-3) stable aggregates. Nanoscopic considerations about the relative stability of clusters with the two different cores are shown to give us new information on the dynamical processes observed in the impact ionization experiments of pure helium clusters and the importance of pre-equilibrium evaporation of the ionic dimers in the ionized clusters.
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Affiliation(s)
- Fabio Marinetti
- Department of Chemistry, University of Rome La Sapienza and CNISM, Piazzale A. Moro 5, 00185 Rome, Italy
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29
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Wang CC, Kornilov O, Gessner O, Kim JH, Peterka DS, Neumark DM. Photoelectron Imaging of Helium Droplets Doped with Xe and Kr Atoms. J Phys Chem A 2008; 112:9356-65. [DOI: 10.1021/jp802332f] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Chia C. Wang
- Department of Chemistry, University of California, Berkeley, California 94720, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Oleg Kornilov
- Department of Chemistry, University of California, Berkeley, California 94720, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Oliver Gessner
- Department of Chemistry, University of California, Berkeley, California 94720, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Jeong Hyun Kim
- Department of Chemistry, University of California, Berkeley, California 94720, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Darcy S. Peterka
- Department of Chemistry, University of California, Berkeley, California 94720, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Daniel M. Neumark
- Department of Chemistry, University of California, Berkeley, California 94720, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
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30
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Bonhommeau D, Lewerenz M, Halberstadt N. Fragmentation of ionized doped helium nanodroplets: theoretical evidence for a dopant ejection mechanism. J Chem Phys 2008; 128:054302. [PMID: 18266445 DOI: 10.1063/1.2823101] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report a theoretical study of the effect induced by a helium nanodroplet environment on the fragmentation dynamics of a dopant. The dopant is an ionized neon cluster Ne(n) (+) (n=4-6) surrounded by a helium nanodroplet composed of 100 atoms. A newly designed mixed quantum/classical approach is used to take into account both the large helium cluster zero-point energy due to the light mass of the helium atoms and all the nonadiabatic couplings between the Ne(n) (+) potential-energy surfaces. The results reveal that the intermediate ionic dopant can be ejected from the droplet, possibly with some helium atoms still attached, thereby reducing the cooling power of the droplet. Energy relaxation by helium atom evaporation and dissociation, the other mechanism which has been used in most interpretations of doped helium cluster dynamics, also exhibits new features. The kinetic energy distribution of the neutral monomer fragments can be fitted to the sum of two Boltzmann distributions, one with a low kinetic energy and the other with a higher kinetic energy. This indicates that cooling by helium atom evaporation is more efficient than was believed so far, as suggested by recent experiments. The results also reveal the predominance of Ne(2) (+) and He(q)Ne(2) (+) fragments and the absence of bare Ne(+) fragments, in agreement with available experimental data (obtained for larger helium nanodroplets). Moreover, the abundance in fragments with a trimeric neon core is found to increase with the increase in dopant size. Most of the fragmentation is achieved within 10 ps and the only subsequent dynamical process is the relaxation of hot intermediate He(q)Ne(2) (+) species to Ne(2) (+) by helium atom evaporation. The dependence of the ionic fragment distribution on the parent ion electronic state reached by ionization is also investigated. It reveals that He(q)Ne(+) fragments are produced only from the highest electronic state, whereas He(q)Ne(2) (+) fragments originate from all the electronic states. Surprisingly, the highest electronic states also lead to fragments that still contain the original ionic dopant species. A mechanism is conjectured to explain this fragmentation inhibition.
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Affiliation(s)
- D Bonhommeau
- University of Minnesota, 207 Pleasant Street S.E., 230 Smith Hall, Minneapolis, Minnesota 55455-0431, USA
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31
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Peterka DS, Kim JH, Wang CC, Poisson L, Neumark DM. Photoionization Dynamics in Pure Helium Droplets. J Phys Chem A 2007; 111:7449-59. [PMID: 17571863 DOI: 10.1021/jp0710032] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photoionization and photoelectron spectroscopy of pure He droplets were investigated at photon energies between 24.6 eV (the ionization energy of He) and 28.0 eV. Time-of-flight mass spectra and photoelectron images were obtained at a series of molecular beam source temperatures and pressures to assess the effect of droplet size on the photoionization dynamics. At source temperatures below 16 K, where there is significant production of clusters with more than 10(4) atoms, the photoelectron images are dominated by fast electrons produced via direct ionization, with a small contribution from very slow electrons with kinetic energies below 1 meV arising from an indirect mechanism. The fast photoelectrons from the droplets have as much as 0.5 eV more kinetic energy than those from atomic He at the same photon energy. This result is interpreted and simulated within the context of a "dimer model", in which one assumes vertical ionization from two nearest-neighbor He atoms to the attractive region of the He2+ potential energy curve. Possible mechanisms for the slow electrons, which were also seen at energies below IE(He), are discussed, including vibrational autoionizaton of Rydberg states comprising an electron weakly bound to the surface of a large HeN+ core.
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Affiliation(s)
- Darcy S Peterka
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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32
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Bonhommeau D, Lake PT, Le Quiniou C, Lewerenz M, Halberstadt N. Modeling the fragmentation dynamics of ionic clusters inside helium nanodroplets: The case of He100Ne4+. J Chem Phys 2007; 126:051104. [PMID: 17302465 DOI: 10.1063/1.2515225] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
We present simulation results on the effect of a helium nanodroplet environment on the fragmentation dynamics of embedded molecular systems. The helium atoms are treated explicitly, with zero-point effects taken into account through an effective helium-helium interaction potential. The ionized neon tetramer is used as a model molecular system because, like all the small rare-gas clusters, it fragments extensively upon ionization. All the nonadiabatic effects between electronic states of the ionized neon cluster are taken into account. The results reveal a predominance of Ne2+ and HepNe2+ fragments and the absence of bare Ne+ fragments, in agreement with available experimental data. The neutral monomer fragments exhibit a rather wide kinetic energy distribution that can be fitted to the sum of two Boltzmann distributions, one with a low kinetic energy and the other with a higher kinetic energy. This indicates that cooling by helium atom evaporation is more efficient than was believed so far, as suggested by recent experimental results. Purely classical calculations are shown to strongly overestimate the amount of cage effect (cooling), clearly indicating the need to take into account zero-point effects.
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Affiliation(s)
- D Bonhommeau
- Laboratoire de Chimie et de Physique Quantiques, IRSAMC, UMR 5626, CNRS et Université Paul Sabatier, 118 route de Narbonne, F-31062 Toulouse Cedex 09, France
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33
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Marinetti F, Coccia E, Bodo E, Gianturco FA, Yurtsever E, Yurtsever M, Yildirim E. Bosonic helium clusters doped by alkali metal cations: interaction forces and analysis of their most stable structures. Theor Chem Acc 2007. [DOI: 10.1007/s00214-006-0240-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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34
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Peterka DS, Kim JH, Wang CC, Neumark DM. Photoionization and Photofragmentation of SF6 in Helium Nanodroplets. J Phys Chem B 2006; 110:19945-55. [PMID: 17020381 DOI: 10.1021/jp062195o] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The photoionization of He droplets doped with SF6 was investigated using tunable vacuum ultraviolet (VUV) synchrotron radiation from the Advanced Light Source (ALS). The resulting ionization and photofragmentation dynamics were characterized using time-of-flight mass spectrometry combined with photofragment and photoelectron imaging. Results are compared to those of gas-phase SF6 molecules. We find dissociative photoionization to SF5+ to be the dominant channel, in agreement with previous results. Key new findings are that (a) the photoelectron spectrum of the SF6 in the droplet is similar but not identical to that of the gas-phase species, (b) the SF5+ photofragment velocity distribution is considerably slower upon droplet photoionization, and (c) fragmentation to SF4+ and SF3+ is much less than in the photoionization of bare SF6. From these measurements we obtain new insights into the mechanism of SF6 photoionization within the droplet and the cooling of the hot photofragment ions produced by dissociative photoionization.
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Affiliation(s)
- Darcy S Peterka
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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