1
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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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2
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Panzou R, Lewerenz M. Photofragmentation of I2 molecules inside helium clusters: model calculations using a quantum effective potential. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1977862] [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]
Affiliation(s)
- Roland Panzou
- Laboratoire Modélisation et Simulation Multi Echelle, MSME, Univ. Gustave Eiffel, CNRS UMR 8208, Univ. Paris Est Créteil, Marne-la-Vallée, France
| | - Marius Lewerenz
- Laboratoire Modélisation et Simulation Multi Echelle, MSME, Univ. Gustave Eiffel, CNRS UMR 8208, Univ. Paris Est Créteil, Marne-la-Vallée, France
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3
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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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4
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Blancafort-Jorquera M, Vilà A, González M. Quantum-classical approach to the reaction dynamics in a superfluid helium nanodroplet. The Ne 2 dimer and Ne-Ne adduct formation reaction Ne + Ne-doped nanodroplet. Phys Chem Chem Phys 2019; 21:24218-24231. [PMID: 31661098 DOI: 10.1039/c9cp04561a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The dynamics of the Ne2 dimer and Ne-Ne adduct formation in a superfluid helium nanodroplet [(4He)N; T = 0.37 K], Ne + Ne@(4He)N→ Ne2@(4He)N'/Ne-Ne@(4He)N' + (N-N')4He with N = 500, has been investigated using a hybrid approach (quantum and classical mechanics (QM-CM) descriptions for helium and the Ne atoms, respectively) and taking into account the angular momentum of the attacking Ne atom, Ne(1). Comparison with zero angular momentum QM results of our own shows that the present results are similar to the quantum ones for the initial Ne(1) velocities (v0) of 500 and 800 m s-1 (the former one being the most probable velocity of Ne at 300 K), in all cases leading to the Ne2 dimer (re = 3.09 Å). However, significant differences appear below v0 = 500 m s-1, because in the QM-CM dynamics, instead of the dimer, a Ne-Ne adduct is formed (r0 = 5.45 Å). The formation of this adduct will probably dominate as the contribution to reactivity of angular momenta larger than zero is the leading one and angular momentum strongly acts against the Ne2 production. Angular momentum adds further difficulties in producing the dimer, since it makes it more difficult to remove the helium density between both Ne atoms to lead, subsequently, to the Ne2 molecule. Hence, the formation of the neon-neon adduct, Ne-Ne@(4He)N', clearly dominates the reactivity of the system, which results in the formation of a "quantum gel"/"quantum foam", because the two Ne atoms essentially maintain their identity inside the nanodroplet. Large enough Ne(1) initial angular momentum values can induce the formation of vortex lines by the collapse of superficial excitations (ripplons), but they occur with greater difficulty than in the case of the capture of the Ne atom by a non doped helium nanodroplet, due to the wave interferences induced by the Ne induced by the solvation layers of the Ne atom originally placed inside the nanodroplet. We hope that this work will encourage other researchers to investigate the reaction dynamics in helium nanodroplets, an interesting topic on which there are few studies available.
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Affiliation(s)
- Miquel Blancafort-Jorquera
- Departament de Ciència de Materials i Química Física and IQTC, Universitat de Barcelona, Martí i Franquès, 1-11, 08028 Barcelona, Spain.
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5
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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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6
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Ozama E, Adachi S, Takayanagi T, Shiga M. Quantum Simulation Verifies the Stability of an 18-Coordinated Actinium-Helium Complex. Chemistry 2018; 24:12716-12721. [DOI: 10.1002/chem.201802554] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Revised: 06/18/2018] [Indexed: 11/10/2022]
Affiliation(s)
- Eiki Ozama
- Department of Chemistry; Saitama University; 255 Shimo-Okubo Sakura-ku Saitama City, Saitama 338-8570 Japan
| | - Sadia Adachi
- Department of Chemistry; Saitama University; 255 Shimo-Okubo Sakura-ku Saitama City, Saitama 338-8570 Japan
| | - Toshiyuki Takayanagi
- Department of Chemistry; Saitama University; 255 Shimo-Okubo Sakura-ku Saitama City, Saitama 338-8570 Japan
| | - Motoyuki Shiga
- Center for Computational Science and E-Systems; Japan Atomic Energy Agency; 148-4, Kashiwanoha, Campus, 178-4 Wakashiba Kashiwa Chiba 277-0871 Japan
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7
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Blancafort-Jorquera M, Vilà A, González M. Quantum-classical dynamics of the capture of neon atoms by superfluid helium nanodroplets. Phys Chem Chem Phys 2018; 20:29737-29753. [DOI: 10.1039/c8cp05140b] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The capture dynamics of Ne by a HeND was studied theoretically in a detailed manner (energy and angular momentum transfer and vortex formation).
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Affiliation(s)
| | - Arnau Vilà
- Departament de Ciència de Materials i Química Física and IQTC
- Universitat de Barcelona
- Barcelona
- Spain
| | - Miguel González
- Departament de Ciència de Materials i Química Física and IQTC
- Universitat de Barcelona
- Barcelona
- Spain
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8
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Seki Y, Takayanagi T, Shiga M. Photoexcited Ag ejection from a low-temperature He cluster: a simulation study by nonadiabatic Ehrenfest ring-polymer molecular dynamics. Phys Chem Chem Phys 2017; 19:13798-13806. [DOI: 10.1039/c7cp00888k] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Nonadiabatic ring-polymer molecular dynamics simulations were performed to understand the photoexcitation dynamics of a low-temperature Ag·He500 cluster.
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Affiliation(s)
- Yusuke Seki
- Department of Chemistry
- Saitama University
- Saitama City
- Japan
| | | | - Motoyuki Shiga
- Center for Computational Science and E-Systems
- Japan Atomic Energy Agency
- Kashiwa
- Japan
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9
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Vilà A, González M. Mass effects in the photodissociation of homonuclear diatomic molecules in helium nanodroplets: inelastic collision and viscous flow energy exchange regimes. Phys Chem Chem Phys 2016; 18:27630-27638. [DOI: 10.1039/c6cp04315a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photodissociation of a diatomic molecule X2 in a superfluid helium nanodroplet presents two sequential dynamic regimes: the starting perfectly inelastic collision followed by the viscous flow. This mechanism has probably general character.
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Affiliation(s)
- Arnau Vilà
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
| | - Miguel González
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
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10
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Vilà A, González M. Reaction dynamics inside superfluid helium nanodroplets: the formation of the Ne2 molecule from Ne + Ne@(4He)N. Phys Chem Chem Phys 2016; 18:31869-31880. [DOI: 10.1039/c6cp03942a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A hybrid TDDFT approach was proposed to consider bimolecular reactive processes in superfluid helium nanodroplets. The Ne + Ne@(4He)N reaction was considered as the first application example. The formation of Ne2 is a complex process related to the nature of the helium density waves and their reflection from the nanodroplet surface.
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Affiliation(s)
- Arnau Vilà
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
| | - Miguel González
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
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11
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Vilà A, González M, Mayol R. Quantum dynamics of the pick up process of atoms by superfluid helium nanodroplets: the Ne + (4He)1000 system. Phys Chem Chem Phys 2016; 18:2006-14. [DOI: 10.1039/c5cp04176g] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The quantum dynamics of neon atom capture by a superfluid helium-4 nanodroplet has been theoretically investigated using a hybrid method.
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Affiliation(s)
- Arnau Vilà
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
| | - Miguel González
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
| | - Ricardo Mayol
- Departament d'Estructura i Constituents de la Matèria
- Universitat de Barcelona
- 08028 Barcelona
- Spain
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12
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Vilà A, González M, Mayol R. Photodissociation Dynamics of Homonuclear Diatomic Molecules in Helium Nanodroplets. The Case of Cl2@(4He)N. J Chem Theory Comput 2015; 11:899-906. [DOI: 10.1021/ct5011642] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Arnau Vilà
- Departament
de Química Física i IQTC and ‡Departament d’Estructura
i Constituents de la Matèria, Universitat de Barcelona, c/Martí
i Franquès, 1, 08028 Barcelona, Spain
| | - Miguel González
- Departament
de Química Física i IQTC and ‡Departament d’Estructura
i Constituents de la Matèria, Universitat de Barcelona, c/Martí
i Franquès, 1, 08028 Barcelona, Spain
| | - Ricardo Mayol
- Departament
de Química Física i IQTC and ‡Departament d’Estructura
i Constituents de la Matèria, Universitat de Barcelona, c/Martí
i Franquès, 1, 08028 Barcelona, Spain
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13
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Vilà A, González M, Mayol R. Quantum interferences in the photodissociation of Cl2(B) in superfluid helium nanodroplets (4He)N. Phys Chem Chem Phys 2015; 17:32241-50. [DOI: 10.1039/c5cp03575a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The origin of quantum interferences theoretically found in the photodissociation of chlorine in superfluid 4He nanodroplets was investigated in detail.
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Affiliation(s)
- Arnau Vilà
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
| | - Miguel González
- Departament de Química Física i IQTC
- Universitat de Barcelona
- 08028 Barcelona
- Spain
| | - Ricardo Mayol
- Departament d’Estructura i Constituents de la Matèria
- Universitat de Barcelona
- 08028 Barcelona
- Spain
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14
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Hauser AW, Gruber T, Filatov M, Ernst WE. Shifts in the ESR spectra of alkali-metal atoms (Li, Na, K, Rb) on helium nanodroplets. Chemphyschem 2013; 14:716-22. [PMID: 23125112 PMCID: PMC3648978 DOI: 10.1002/cphc.201200697] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2012] [Revised: 10/15/2012] [Indexed: 11/06/2022]
Abstract
He-droplet-induced changes of the hyperfine structure constants of alkali-metal atoms are investigated by a combination of relativistically corrected ab initio methods with a simulation of the helium density distribution based on He density functional theory. Starting from an accurate description of the variation of the hyperfine structure constant in the M-He diatomic systems (M=Li, Na, K, Rb) as a function of the interatomic distance we simulate the shifts induced by droplets of up to 10,000 (4)He atoms. All theoretical predictions for the relative shifts in the isotropic hyperfine coupling constants of the alkali-metal atoms attached to helium droplets of different size are then tied to a single, experimentally derived parameter of Rb.
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Affiliation(s)
- Andreas W Hauser
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria.
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15
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A practical approach to temperature effects in dissociative electron attachment cross sections using local complex potential theory. Chem Phys 2012. [DOI: 10.1016/j.chemphys.2012.08.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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16
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Poms J, Hauser AW, Ernst WE. Helium nanodroplets doped with xenon and rubidium atoms: a case study of van der Waals interactions between heliophilic and heliophobic dopants. Phys Chem Chem Phys 2012; 14:15158-65. [DOI: 10.1039/c2cp42333b] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Hernando A, Barranco M, Pi M, Loginov E, Langlet M, Drabbels M. Desorption of alkali atoms from 4He nanodroplets. Phys Chem Chem Phys 2012; 14:3996-4010. [DOI: 10.1039/c2cp23526a] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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18
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TAKAYANAGI TOSHIYUKI, SHIGA MOTOYUKI, TAKETSUGU TETSUYA. DEVELOPMENT OF A THREE-DIMENSIONAL AB INITIO POTENTIAL ENERGY SURFACE FOR THE He–Cl2(X) SYSTEM AND ITS APPLICATION TO SOLVATION STRUCTURES IN THE HenCl2 CLUSTERS. JOURNAL OF THEORETICAL & COMPUTATIONAL CHEMISTRY 2011. [DOI: 10.1142/s0219633605001295] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
High-quality ab initio electronic structure calculations for the van der Waals interaction of He with Cl 2 in the electronic ground state have been carried out to develop a new three-dimensional potential energy surface for this system. The calculations were performed at the single and double excitation coupled-cluster level of theory with non-iterative perturbational treatment of triple excitations [CCSD(T)] with a very large basis set including an additional set of bond functions. The analytical potential surface developed were then used in the path-integral molecular dynamics calculations for the He n Cl 2 cluster, where quantum solvation structures of helium atoms in clusters were investigated. It has been found that the helium solvation structures are quite different between the electronic ground state and the electronically excited B 3Π state.
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Affiliation(s)
| | - MOTOYUKI SHIGA
- Center for Promotion of Computational Science and Engineering, Japan Atomic Energy Research Institute, Tokyo 110-0015, Japan
| | - TETSUYA TAKETSUGU
- Department of Chemistry, Ochanomizu University, Tokyo 112-8610, Japan
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19
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Giese C, Stienkemeier F, Mudrich M, Hauser AW, Ernst WE. Homo- and heteronuclear alkali metal trimers formed on helium nanodroplets. Part II. Femtosecond spectroscopy and spectra assignments. Phys Chem Chem Phys 2011; 13:18769-80. [PMID: 21869967 DOI: 10.1039/c1cp21191a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Homo- and heteronuclear alkali quartet trimers of type K(3-n)Rb(n) (n = 0,1,2,3) formed on helium nanodroplets are probed by one-color femtosecond (fs) photoionization (PI) spectroscopy. The obtained frequencies are assigned to vibrations in different electronic states in comparison to high level ab initio calculations of the involved potentials including pronounced Jahn-Teller and spin-orbit couplings. Despite the fact that the resulting complex vibronic structure of the heavy alkali molecules complicates the comparison of experiment and theory we find good agreement for many of the observed lines for all species.
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Affiliation(s)
- Christian Giese
- Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany.
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20
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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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21
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Braun A, Drabbels M. Photodissociation of alkyl iodides in helium nanodroplets. III. Recombination. J Chem Phys 2007; 127:114305. [PMID: 17887835 DOI: 10.1063/1.2767263] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The recombination of fragments resulting from the photodissociation of (fluorinated) alkyl iodides in helium nanodroplets at a wavelength of 266 nm has been investigated by means of ion imaging techniques. It is found that in the case of CH3I an appreciable fraction of the fragments recombine in the aftermath of the photolysis. The proposed mechanism involves a complete translational relaxation of both photofragments inside the nanodroplets followed by geminate recombination of the fragments. In contrast with CH3I, no recombination is observed for CF3I. This is attributed to the larger masses and the different initial kinetic energies of the fragments produced by the photolysis of CF3I, which strongly diminishes the fragment thermalization efficiency.
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Affiliation(s)
- Andreas Braun
- Laboratoire de Chimie Physique Moléculaire, Ecole Polytechnique Fédéral de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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22
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Braun A, Drabbels M. Photodissociation of alkyl iodides in helium nanodroplets. I. Kinetic energy transfer. J Chem Phys 2007; 127:114303. [PMID: 17887833 DOI: 10.1063/1.2767261] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The photodissociation of (fluorinated) alkyl iodides in helium nanodroplets at a wavelength of 266 nm has been investigated by means of ion imaging techniques. It is found that a significant fraction of the created fragments escapes from the helium droplets. The speed and kinetic energy distributions of these fragments are found to be notably modified with respect to the corresponding gas phase distributions. The fragments, furthermore, show a speed dependent angular distribution. The loss of kinetic energy as well as the reduction of the anisotropy parameter show a strong mass dependence. These observations point to a nonthermal escape process in which the kinetic energy and momentum transfer from the fragments to the solvent is governed by binary collisions with the individual helium atoms making up the droplet. Monte Carlo simulations based on hard-sphere binary collisions substantiate this interpretation of the data.
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Affiliation(s)
- Andreas Braun
- Laboratoire de Chimie Physique Moléculaire, Ecole Polytechnique Fédéral de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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23
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Loginov E, Drabbels M. Excited State Dynamics of Ag Atoms in Helium Nanodroplets. J Phys Chem A 2007; 111:7504-15. [PMID: 17569515 DOI: 10.1021/jp0716278] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The excited state dynamics of silver atoms embedded in helium nanodroplets have been investigated by a variety of spectroscopic techniques. The experiments reveal that 5p 2P1/2 <-- 5s 2S1/2 excitation of embedded silver atoms results almost exclusively in the ejection of silver atoms populating the 2P1/2 state. In contrast, excitation to the 5p 2P3/2 state leads to the ejection of not only silver atoms in the 2P1/2, 2P3/2, and 2D5/2 excited states but also of AgHe and AgHe2. These AgHe exciplexes are mainly formed in the A2Pi1/2 electronic state. In addition, it is found that a considerable fraction of the 2P3/2 excited silver atoms become solvated within the helium droplets, most probably as AgHe2. The observations can be accounted for by a model in which the metastable 2D5/2 state of silver acts as a doorway state in the relaxation of 2P3/2 excited silver atoms.
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Affiliation(s)
- Evgeniy Loginov
- Laboratoire de Chimie Physique Moléculaire, Ecole Polytechnique Fédéral de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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24
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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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Tiggesbäumker J, Stienkemeier F. Formation and properties of metal clusters isolated in helium droplets. Phys Chem Chem Phys 2007; 9:4748-70. [PMID: 17712454 DOI: 10.1039/b703575f] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The unique conditions forming atomic and molecular complexes and clusters using superfluid helium nanodroplets have opened up an innovative route for studying the physical and chemical properties of matter on the nanoscale. This review summarizes the specific characteristics of the formation of atomic clusters partly generated far from equilibrium in the helium environment. Special emphasis is on the optical response, electronic properties as well as dynamical processes which are mostly affected by the surrounding quantum matrix. Experiments include the optical induced response of isolated cluster systems in helium under quite different excitation conditions ranging from the linear regime up to the violent interaction with a strong laser field leading to Coulomb explosion and the generation of highly charged atomic fragments. The variety of results on the outstanding properties in the quantum size regime highlights the peculiar capabilities of helium nanodroplet isolation spectroscopy.
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Bonhommeau D, Halberstadt N, Viel A. Fragmentation dynamics of ionized neon clusters (Nen,n=3–14) embedded in helium nanodroplets. J Chem Phys 2006; 124:024328. [PMID: 16422604 DOI: 10.1063/1.2158993] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
We report a theoretical study of the nonadiabatic fragmentation dynamics of ionized neon clusters embedded in helium nanodroplets for cluster sizes up to n=14 atoms. The dynamics of the neon atoms is modeled using the molecular dynamics with quantum transitions method of Tully [J. Chem. Phys. 93, 1061 (1990)] with the nuclei treated classically and transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model to which induced dipole-induced dipole interactions are added. The effect of the spin-orbit interaction is also discussed. The helium environment is modeled by a friction force acting on charged atoms whose speed exceeds the critical Landau velocity. The dependence of the fragment size distribution on the friction strength and on the initial nanodroplet size is investigated. By comparing with the available experimental data obtained for Ne3+ and Ne4+, a reasonable value for the friction coefficient, the only parameter of the model, is deduced. This value is then used to predict the effect of the helium environment on the dissociation dynamics of larger neon clusters, n=5-14. The results show stabilization of larger fragments than in the gas phase, but fragmentation is not completely caged. In addition, two types of dynamics are characterized for Ne4+: fast and explosive, therefore leaving no time for friction to cool down the process when dynamics starts on one of the highest electronic states, and slower, therefore leading to some stabilization by helium when it starts on one of the lowest electronic states.
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Affiliation(s)
- David Bonhommeau
- Laboratoire de Physique Quantique, IRSAMC, UMR 5626, CNRS et Université Paul Sabatier, F-31062 Toulouse Cedex 09, France
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Lewis WK, Bemish RJ, Miller RE. Fragmentation of HCN in optically selected mass spectrometry: Nonthermal ion cooling in helium nanodroplets. J Chem Phys 2005; 123:141103. [PMID: 16238367 DOI: 10.1063/1.2046672] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
A technique that combines infrared laser spectroscopy and helium nanodroplet mass spectrometry, which we refer to as optically selected mass spectrometry, is used to study the efficiency of ion cooling in helium. Electron-impact ionization is used to form He(+) ions within the droplets, which go on to transfer their charge to the HCN dopant molecules. Depending upon the droplet size, the newly formed ion either fragments or is cooled by the helium before fragmentation can occur. Comparisons with gas-phase fragmentation data suggest that the cooling provided by the helium is highly nonthermal. An "explosive" model is proposed for the cooling process, given that the initially hot ion is embedded in such a cold solvent.
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Affiliation(s)
- William K Lewis
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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Braun A, Drabbels M. Imaging the translational dynamics of CF3 in liquid helium droplets. PHYSICAL REVIEW LETTERS 2004; 93:253401. [PMID: 15697895 DOI: 10.1103/physrevlett.93.253401] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2004] [Indexed: 05/24/2023]
Abstract
The translational dynamics of CF3 in liquid helium have been investigated by photodissociating CF3I dissolved in helium droplets consisting of several thousands of atoms. The velocity distribution of CF3 fragments that have escaped from the droplets has been determined using ion imaging techniques and is found to be considerably shifted to lower speeds with respect to the photodissociation of gas phase CF3I. The fragments furthermore show a speed dependent angular distribution that is isotropic for the slowest and approaches the gas phase distribution for the faster fragments. These distributions point to a nonthermal escape process in which, at least for the speeds relevant for the present experiment, the kinetic energy and momentum transfer from the fragments to the solvent appears to be governed by binary collisions with the individual helium atoms.
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Affiliation(s)
- Andreas Braun
- Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology Lausanne, CH-1015 Lausanne, Switzerland
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Wada A, Takayanagi T, Shiga M. Theoretical simulations on photoexcitation dynamics of the silver atom embedded in helium clusters. J Chem Phys 2003. [DOI: 10.1063/1.1599351] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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