| 1. |
- Adams, Christopher, et al.
(författare)
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Vibrational Autodetachment from Anionic Nitroalkane Chains - From Molecular Signatures to Thermionic Emission
- 2019
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 123:40, s. 8562-8570
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Tidskriftsartikel (refereegranskat)abstract
- We report the kinetic energy distributions in electron autodetachment from nitroethane, 1-nitropropane, and 1-nitrobutane anions upon laser excitation of CH stretching modes measured using velocity map electron imaging. In striking contrast to the case of nitromethane, the kinetic energy distributions show almost no distinct vibrational features, and they can be described by thermionic emission, relating the shape of the distributions to the electron capture cross section of the neutral molecule. The data suggest that a classical description is warranted above ca. 20 meV electron kinetic energy. At lower energies, quantum effects suppress the attachment cross section.
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| 2. |
- Anderson, Emma K., et al.
(författare)
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Decays of excited silver-cluster anions Agn, n=4 to 7, in the Double ElectroStatic Ion Ring ExpEriment
- 2018
-
Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 98:2
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Tidskriftsartikel (refereegranskat)abstract
- Spontaneous decays of small, hot silver-cluster anions Ag-n(-), n = 4-7, have been studied using one of the rings of the Double ElectroStatic Ion Ring ExpEriment (DESIREE). Observation of these decays over very long time scales is possible due to the very low residual gas pressure (similar to 10(-14)) and cryogenic (13 K) operation of DESIREE. The yield of neutral particles from stored beams of Ag-6(-) and Ag-2(-) anions were measured for 100 milliseconds and were found to follow single power-law behavior with millisecond time-scale exponential cutoffs. The Ag-4(-) and Ag-5(-) anions were stored for 60 s and the observed decays show two-component power-law behaviors. We present calculations of the rate constants for electron detachment from and fragmentation of Ag-4(-) and Ag-5(-). In these calculations, we assume that the internal energy distribution of the clusters are flat and with this we reproduce the early steep parts of the experimentally measured decay curves for Ag-4(-) and Ag-5(-) which extends to tens and hundreds of milliseconds, respectively. The fact that the calculations reproduce the early slopes of Ag-4(-) and Ag-5(-), which differ for the two cases, suggests that it is the changes in fragmentation rates with internal cluster energies of Ag-4(-) and Ag-5(-) rather than conditions in the ion source that determine this behavior. Comparisons with the measurements strongly suggest that the neutral particles detected in these time domains originate from Ag-4(-) -> Ag-3(-) + Ag and Ag-5(-) -> Ag-3(-) +Ag-2 fragmentation processes.
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| 3. |
- Barillot, T., et al.
(författare)
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Angular asymmetry and attosecond time delay from the giant plasmon resonance in C60 photoionization
- 2015
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 91
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Tidskriftsartikel (refereegranskat)abstract
- This combined experimental and theoretical study demonstrates that the surface plasmon resonance in C 60 alters the valence photoemission quantum phase, resulting in strong effects in the photoelectron angular distribution and emission time delay. Electron momentum imaging spectroscopy is used to measure the photoelectron angular distribution asymmetry parameter that agrees well with our calculations from the time-dependent local density approximation (TDLDA). Significant structure in the valence photoemission time delay is simultaneously calculated by TDLDA over the plasmon active energies. Results reveal a unified spatial and temporal asymmetry pattern driven by the plasmon resonance and offer a sensitive probe of electron correlation. A semiclassical approach facilitates further insights into this link that can be generalized and applied to other molecular systems and nanometer-sized metallic materials exhibiting plasmon resonances.
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| 4. |
- Chen, Fuqiang, et al.
(författare)
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Radiative cooling of cationic carbon clusters, CN+, N=8,10,13-16
- 2019
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Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21, s. 1587-1596
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Tidskriftsartikel (refereegranskat)abstract
- The radiative cooling of highly excited carbon cluster cations of sizes N = 8, 10, 13–16 has been studied in an electrostatic storage ring. The cooling rate constants vary with cluster size from a maximum at N = 8 of 2.6 × 104 s−1 and a minimum at N = 13 of 4.4 × 103 s−1. The high rates indicate that photon emission takes place from electronically excited ions, providing a strong stabilizing cooling of the molecules.
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| 5. |
- Ferrari, Piero, et al.
(författare)
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Radiative cooling of size-selected gas phase clusters
- 2019
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Ingår i: International reviews in physical chemistry. - 0144-235X .- 1366-591X. ; 38:3-4, s. 405-440
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Tidskriftsartikel (refereegranskat)abstract
- Predicted almost forty years ago, the radiation from thermally populated excited electronic states has recently been recognised as an important cooling mechanism in free molecules and clusters. It has presently been observed from both inorganic clusters and carbonbased molecules in molecular beams and ion storage devices. Experiments have demonstrated that many of these systems radiate at rates approaching microsecond time scales, and often with a distinct dependence on the precise number of atoms in the system. The radiation acts as a strongly stabilising factor against both unimolecular decay and thermal electron emission. In astrophysical context, radiative cooling provides a mechanism to dissipate internal energy in star-forming processes, and stabilises molecules selectively in the circumstellar medium. The consequences of an active radiative cooling channel for nanoparticle production will likewise favour special sizes in non-equilibrium formation processes. In this review, the radiative cooling of clusters is presented and illustrated with examples of experiments performed on small carbon, metal, and semiconductor clusters, and on PAH molecules. The experimental and theoretical techniques used are discussed, together with the consequences of radiative cooling on size-to-size stability patterns of clusters.
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| 6. |
- Ferrari, P., et al.
(författare)
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Stability of small cationic platinum clusters
- 2018
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 10:46, s. 29085-29090
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Tidskriftsartikel (refereegranskat)abstract
- The relative stability of small cationic platinum clusters is investigated by photofragmentation experiments. Mass spectra show a smooth intensity distribution except for a local intensity minimum at Pt-5(+), revealing enhanced stability of the platinum tetramer Pt-4(+). The possibility that radiative cooling competes with statistical fragmentation after photoexcitation is examined and it is shown that clusters in the N = 3-8 size range do not radiate on the time scale of the experiment. In the absence of radiative cooling, the mass spectra of photofragmented clusters can be well explained by dissociation energies computed using density functional theory. The large calculated HOMO-LUMO gap for Pt-4(+) (approximate to 1.2 eV) is attributed to its highly symmetric structure and provides an explanation for the surprisingly low reactivity of this cluster in different gas-phase reactions.
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| 7. |
- Ferrari, Piero, et al.
(författare)
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The effect of radiative cooling on the size-dependent stability of small boron clusters
- 2018
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 98
-
Tidskriftsartikel (refereegranskat)abstract
- The mass spectrum of cationic boron clusters, BN+ (N = 5 − 20), after photoexcitation demonstrates that radiative cooling is an important, though often neglected, process in determining the relative stability of small and isolated particles. The observed intensities inmass spectra suggest that B5+, B11+, B13+, and B15+ are particularly stable clusters, consistent with density-functional theory calculations. Quantitative agreement, however, is only obtained if radiative cooling is included in the analysis.All clusters are found to radiate onmicrosecond timescales, suggesting recurrent fluorescence as the dominant photon emission process.
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| 8. |
- Ferrari, Piero, et al.
(författare)
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Thermal radiation and fragmentation pathways of photo-excited silicon clusters
- 2015
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:22
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation of laser heated silicon clusters was studied by time-of-flight mass spectrometry. For Si+n (n = 5–19, 21), the lowest energy fragmentation pathways were identified as the metastable decay channel occurring after the primary acceleration of the ions. The radiative cooling of laser excited Si+n (n = 5–9, 11, and 13) was quantified via its quenching effect on the amount of metastable fragmentation. The quenching varied strongly with cluster size, from no observable amount for Si+7 to a cooling constant of 3 · 10E5 s−1 for Si+13. In addition, based on the observed fragmentation channels, the ionization energies and the relative binding energies of the clusters were partially ordered, and several ionization energies have been bracketed more precisely.
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| 9. |
- Furukawa, T., et al.
(författare)
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Cooling dynamics of photo-excited negative carbon cluster ions stored in an ion storage ring
- 2015
-
Ingår i: Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 354, s. 192-196
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Tidskriftsartikel (refereegranskat)abstract
- A newly found fast radiative cooling process of C-6(-) is studied by simulation based on statistical sharing of the internal energy by the vibrational modes both in the electronic ground and excited states. For comparison, a contrasting slow cooling of C6H- is simulated by the same procedure. The simulation demonstrates a distinct difference in the time evolution of energy distributions between C-6(-) and C6H-, and well reproduces the observed fast cooling of C-6(-) by recurrent electronic transitions and the slow cooling of C6H- by vibrational de-excitation. (C) 2014 Elsevier B.V. All rights reserved.
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| 10. |
- Hansen, Klavs, 1958
(författare)
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Action spectroscopy of highly excited molecular ions in molecular beams
- 2018
-
Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 430, s. 14-21
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Tidskriftsartikel (refereegranskat)abstract
- The use of action spectroscopy for quantitative comparisons of different parts of a recorded spectrumrequires that the efficiency of the emission process after photon absorption is quantitatively known. Thequantum yields of measured photo-dissociation processes after photo-absorption are derived here formolecular beams with broad energy distributions. The effect of radiative cooling on the yield is included.The quantum yield for both low energy photons and radiative species shows large variations with photonenergy.
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| 11. |
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| 12. |
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| 13. |
- Hansen, Klavs, 1958
(författare)
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Description of unimolecular reaction rates of Lennard-Jones clusters
- 2019
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 52
-
Tidskriftsartikel (refereegranskat)abstract
- The unimolecular rate constant of Lennard-Jones clusters with N=54−56 atoms has been investigated in constant energy molecular dynamics simulations and compared with the detailed balance predictions. Decays were found to be statistical and absolute rate constants agree quantitatively with detailed balance predictions. The level densities required for the comparison of simulated and calculated rate constants were obtained from separate simulations using the integrated microcanonical temperature. The quantitative agreement between simulations and theory requires that the classical degeneracy of the ground state is included into the level densities.
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| 14. |
- Hansen, Klavs, 1958, et al.
(författare)
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Detection of Recurrent Fluorescence Photons
- 2016
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 117
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Tidskriftsartikel (refereegranskat)abstract
- We have detected visible photons emitted from the thermally populated electronic excited state, namely recurrent fluorescence (RF), of C−6 stored in an electrostatic ion storage ring. Clear evidence is provided to distinguish RF from normal fluorescence, based on the temporal profile of detected photons synchronized with the revolution of C−6 in the ring, for which the time scale is far longer than the lifetime of the intact photoexcited state. The relaxation (cooling) process via RF is likely to be commonplace for isolated molecular systems and crucial to the stabilization of molecules in interstellar environments.
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| 15. |
- Hansen, Klavs, 1958, et al.
(författare)
-
Energy flow in peptides after UV photoexcitation of backbone linkages
- 2017
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Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:30, s. 19640-5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the dissociation channels after UV photoexcitation of peptide cations tagged with 18-crown-6 ether (CE). The model peptides chosen for study were singly protonated (Ala)n–Pro (n = 1, 2, 3) and Pro–Pro (Ala = alanine, Pro = proline) that all contain at least one tertiary amide group with high absorption cross section at 210 nm (5.90 eV). Statistical dissociation was identified from the loss of CE, a process occuring remotely from the initial site of excitation, and therefore requiring flow of energy to the ammonium group where the CE is bound. However, homolytic breakage of the peptide backbone at the site of excitation is competitive, resulting in so-called a radical cations. Density functional theory calculations of dissociation energies were done on the simplest system [Ala–Pro + H+](CE) and found to be 1.87 eV for CE loss and 3.29 eV for the formation of a+(CE) and x. These numbers were used to calculate statistical branching ratios for the dissociation processes based on detailed balance. After the absorption of two 210 nm photons (according to power-dependence measurements), the branching ratio between the two channels is calculated to be less than 10E-4, far below the observed ratio of 0.65. Hence both statistical and non-statistical dissociation contribute to dissociation of these photoexcited peptides.
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| 16. |
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| 17. |
- Hansen, Klavs, 1958, et al.
(författare)
-
Gold Cluster Electronic Radiative Cooling and Abundances
- 2017
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:20, s. 10663-10669
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Tidskriftsartikel (refereegranskat)abstract
- The effect on abundances of radiative cooling of gold clusters is analyzed quantitatively for cluster sizes n = 8-20 based on known dissociation energies, radiative time Constants and the monomer unimoledilar decay frequency factor, and an assumed dimer loss frequency factor. Radiative cooling is observed to quench the temporal development of the abundance spectra and, in general, to produce larger size-to-size contrasts than observed in the absence of radiation. Also, the emission of photons with large and small energies was compared quantitatively. For small photon energies, the radiative time constant is not given by the photon emission rate constant. An alternative expression for this regime was found to be very accurate. Strong radiative cooling will have consequences both for the interpretation of mass abundance spectra and potentially also for the production of specific mass selected nanoparticles. The present work supplies the conceptual framework for such applications.
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| 18. |
- Hansen, Klavs, 1958, et al.
(författare)
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Influence of thermal radiation on hot cluster decay rates and abundances
- 2019
-
Ingår i: Chinese Journal of Chemical Physics. - : AIP Publishing. - 1674-0068 .- 2327-2244. ; 32:2, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- The influence of radiative cooling on the unimolecular decay rates of free, hot clusters and molecules with unspecified excitation energies is quantified. Two different regimes, defined by the magnitude of the energy of the photons emitted, are identified and the boundary between them is given. The boundary is determined in terms of the photon emission rate constants and thermal properties of the particles. Also the abundance spectra are calculated for the continuous cooling case, corresponding to small photon energies. The two regimes correspond to continuous cooling and single photon quenching of the unimolecular decay. The radiative effect can be parametrized by a redefinition of the time each individual cluster has available to undergo evaporation, expressed by an effective radiative time constant.
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| 19. |
- Hansen, Klavs, 1958, et al.
(författare)
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Ionisering af store molekyler
- 2017
-
Ingår i: KVANT. - 0905-8893. ; 28:3, s. 17-20
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Ionisering er en fundamental proces i naturen. Overraskende nok dukker der stadig nye versioner af processen op. Denne artikel beskriver den sidste nye, som blev præsenteret for verden i begyndelsen af 2017.
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| 20. |
- Hansen, Klavs, 1958, et al.
(författare)
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Magic numbers and stabilities of heavy water clusters,(D2O)ND+, N = 3 −48
- 2019
-
Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 440, s. 14-19
-
Tidskriftsartikel (refereegranskat)abstract
- The abundance spectrum of deuterated heavy water clusters has been measured, and relative dissociationenergies were extracted from the abundances. The dissociation energies are similar to those of protonatedlight water clusters, except for a slightly reduced excess stability of the N = 21 cluster relative to the N = 22cluster. The difference is interpreted in terms of the special geometry of the N = 21 cluster. The absenceof a similar effect for N = 28/29 suggests that the stability of the N = 28 cluster is not due to a closed shellstructure
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| 21. |
- Hansen, Klavs, 1958, et al.
(författare)
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Non-scrambling of hydrogen in NH 4 + (H 2 O) 3 clusters
- 2019
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 9:12, s. 6620-6626
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the metastable decay of protonated, ammonia-doped, deuterated water clusters produced in an electrospray source, dn-NH4+(H2O)3, n = 0-6. The mass spectra show a very strong odd-even effect, consistent with a low degree of scrambling of the hydrogen bound to water and to the ammonia. The relative evaporation rate constant for light water was almost twice the one for heavy water, with the rate for mixed protium-deuterium water molecule intermediate between these two values.
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| 22. |
- Hansen, Klavs, 1958, et al.
(författare)
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Non-scrambling of hydrogen in NH4+(H2O)3 clusters
- 2019
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 9, s. 6620-6626
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the metastable decay of protonated, ammonia-doped, deuterated water clusters produced in an electrospray source, dn-NH4 +(H2O)3, n ¼ 0–6. The mass spectra show a very strong odd–even effect, consistent with a low degree of scrambling of the hydrogen bound to water and to the ammonia. The relative evaporation rate constant for light water was almost twice the one for heavy water, with the rate for mixed protium–deuterium water molecule intermediate between these two values.
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| 23. |
- Hansen, Klavs, 1958, et al.
(författare)
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Single Photon Thermal Ionization of C60
- 2017
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 118
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Tidskriftsartikel (refereegranskat)abstract
- We report on experiments which show that C60 can ionize in an indirect, quasithermal boiloff process after absorption of a single photon. The process involves a large number of incoherently excited valence electrons and yields electron spectra with a Boltzmann distribution with temperatures exceeding 104 K. It is expected to be present for other molecules and clusters with a comparatively large number of valence electrons. The astrophysical consequences are briefly discussed.
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| 24. |
- Hansen, Klavs, 1958, et al.
(författare)
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Single photon thermal ionization of large molecules
- 2017
-
Ingår i: Elettra Highlights.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have demonstrated that gas phase C60 can ionize in a quasi-thermal process where the absorption of a single photon at energies of several tens of eVs leads to the formation of a transient hot electron gas, while the vibrational degrees of freedom remain cold. The existence of the hot electron gas is signalled by the emission of thermal electrons with Boltzmann-like kinetic energy distributions with temperatures of 10000−20000 K. The ionization mechanism is expected to be general for large molecules and will have, e.g., astrophysical consequences.
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| 25. |
- Hansen, Klavs, 1958
(författare)
-
Single photon transient hot electron ionization of C60
- 2017
-
Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:30, s. 19699-19706
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Tidskriftsartikel (refereegranskat)abstract
- Recent experiments have demonstrated that C60 can ionize in a thermal process after absorption of a photon with energy far above the ionization energy. This indirect ionization mechanism is investigated here by calculating the total and singly charged ion yields, electron energy distributions, and effective electronic temperatures as a function of photon energy.
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| 26. |
- Hansen, Klavs, 1958, et al.
(författare)
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Spontaneous decay of small copper-cluster anions Cun− (n=3–6), on long time scales
- 2017
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 95:2
-
Tidskriftsartikel (refereegranskat)abstract
- We have measured the spontaneous neutral particle emission from copper-cluster anions (Cun −, n = 3–6) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The measured rate of emission from the stored Cu3 − ions follows a single power-law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu3 as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu4 −, Cu5−, and Cu6− are well described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu6− ions that were excited by 1.13- or 1.45-eV photons after 46 ms of storage.
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| 27. |
- Hansen, Klavs, 1958
(författare)
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Statistical physics of nanoparticles in the gas phase
- 2018
-
Bok (övrigt vetenskapligt/konstnärligt)abstract
- Several changes have been made to the text in this second edition relative to the first, and no chapter has been left untouched in the process. The changes are of two types. One is an expansion of the scope of the material covered. The other is the introduction of new developments of the field. The revisions have resulted in two new chapters and several new sections. In addition to these changes, uncountably many minor changes have been made in figures and in the text to improve readability. A part of the preparation of this edition was the correction of the errors and (mostly) misprints spotted in the first edition. During this process, it became clear to me that while two errors may cancel each other, mistakes never do. Happily, most mistakes were of minor importance. The idea behind the book remains unchanged: To provide a guided tour of a number of interesting phenomena in the field. A reader who compares this edition with the first will realize that occasionally the presentation has changed radically. But although the flavor may have changed here and there, hopefully the nutritional value still makes it worth for the reader to consume the dish. I want to thank Takeshi Furukawa, Bernd von Issendorff, Vitali Zhaunerchyk, and Mathias Weber for providing illustrative experimental data; Petr Slavícĕk for an educational conversation on holy water at an Erice Workshop; and Hanna Vehkamäki for enlightening me on the first nucleation theorem. Corrections, suggestions, and error reports are welcome and can be mailed to me at klavshansen@tju.edu.cn.
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| 28. |
- Hansen, Klavs, 1958
(författare)
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The classical capture cross section of an electron and neutral and anionic polarizable molecules with permanent dipole moments
- 2019
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 438, s. 142-147
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Tidskriftsartikel (refereegranskat)abstract
- tThe energy dependent capture cross sections of electrons and polarizable neutral molecules with perma-nent dipole moments and with and without an additional negative charge are calculated classically. Theresults can be expressed in lengths and energies scaled with parameters that derive from the polarizabil-ity, dipole moment and charge. Cross sections integrated over impact angles are given. The results are ofinterest for both electron attachment and for thermal electron emission. The consequences for thermalelectron emission spectra are discussed quantitatively.
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| 29. |
- Hansen, Klavs, 1958
(författare)
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The effective temperature in microcanonical rate constants
- 2015
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 620, s. 43-45
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Tidskriftsartikel (refereegranskat)abstract
- Microcanonical rate constants can be parameterized in terms of an effective temperature. We show here that for fairly general level densities of the involved species it is possible to make this parametrization with a temperature independent heat capacity and a rate constant of the Arrhenius form. This is a major simplification in the interpretation of many experiments on unimolecular decay in vacuum. The results show that activation energies and heat capacities measured in microcanonical experiment differ from their canonical analogues.
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| 30. |
- Hansen, Klavs, 1958, et al.
(författare)
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Thermal radiation of gold clusters on microsecond time scales
- 2017
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 96
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Tidskriftsartikel (refereegranskat)abstract
- Small positively charged gold clusters have been found to emit thermal radiation at a very high rate, with time constants ranging from one to 35μs for Aun + (n = 6–13,15). For sizes n = 14,16–20 the radiation occurs on much longer time scales. Strong thermal suppression of the population of higher-lying states puts constraints on the possible energies of excited states that can contribute to the radiation. Taking that into account, an evaluation of the experimentally determined rate constants shows that the strong radiation originates from thermally excited low-lying electronic states hitherto not observed. The origin of these states is discussed and two possibilities are suggested: one is related to electron correlation and electron pairing, and the other results from thermal shape fluctuations.
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| 31. |
- Hansen, Klavs, 1958
(författare)
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Tunneling and reflection in unimolecular reaction kinetic energy release distributions
- 2018
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 693, s. 66-71
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Tidskriftsartikel (refereegranskat)abstract
- The kinetic energy release distributions in unimolecular reactions is calculated with detailed balance theory, taking into account the tunneling and the reflection coefficient in three different types of transition states; (i) a saddle point corresponding to a standard RRKM-type theory, (ii) an attachment Langevin cross section, and (iii) an absorbing sphere potential at short range, without long range interactions. Corrections are significant in the one dimensional saddle point states. Very light and lightly bound absorbing systems will show measurable effects in decays from the absorbing sphere, whereas the Langevin cross section is essentially unchanged.
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| 32. |
- Hansen, Mette, et al.
(författare)
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Effect of Whey Protein Hydrolysate on Performance and Recovery of Top-Class Orienteering Runners.
- 2015
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Ingår i: International Journal of Sport Nutrition & Exercise Metabolism. - : Human Kinetics. - 1526-484X .- 1543-2742. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- This trial aimed to examine the effect of whey protein hydrolysate intake before and after exercise sessions on endurance performance and recovery in elite orienteers during a training camp. Eighteen elite orienteers participated in a randomized controlled intervention trial during a 1-week training camp (13 exercise sessions). Half of the runners (PRO-CHO) ingested a protein drink before (0.3 g kg−1) and a protein-carbohydrate drink after (0.3 g protein kg−1 and 1 g carbohydrate kg−1) each exercise session. The others ingested energy and timematched carbohydrate drinks (CHO). A 4-km run-test with 20 control points was performed before and on the last day of the intervention. Blood and saliva were obtained in the mornings, before and after run-tests, and after the last training session. During the intervention, questionnaires were fulfilled regarding psychological sense of performance capacity and motivation. PRO-CHO and not CHO improved performance in the 4-km run-test (interaction p < .05). An increase in serum creatine kinase was observed during the week, which was greater in CHO than PRO-CHO (interactionp < .01). Lactate dehydrogenase (p < .001) and cortisol (p = .057) increased during the week, but the change did not differ between groups. Reduction in sense of performance capacity during the intervention was greater in CHO (p < .05) than PRO-CHO. In conclusion, ingestion of whey protein hydrolysate before and after each exercise session improves performance and reduces markers of muscle damage during a strenuous 1-week training camp. The results indicate that protein supplementation in conjunction with each exercise session facilitates the recovery from strenuous training in elite orienteers.
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| 33. |
- Hansen, M., et al.
(författare)
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Protein intake during training sessions has no effect on performance and recovery during a strenuous training camp for elite cyclists
- 2016
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Ingår i: Journal of the International Society of Sports Nutrition. - : Informa UK Limited. - 1550-2783. ; 13:9
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Tidskriftsartikel (refereegranskat)abstract
- Background: Training camps for top-class endurance athletes place high physiological demands on the body. Focus on optimizing recovery between training sessions is necessary to minimize the risk of injuries and improve adaptations to the training stimuli. Carbohydrate supplementation during sessions is generally accepted as being beneficial to aid performance and recovery, whereas the effect of protein supplementation and timing is less well understood. We studied the effects of protein ingestion during training sessions on performance and recovery of elite cyclists during a strenuous training camp. Methods: In a randomized, double-blinded study, 18 elite cyclists consumed either a whey protein hydrolysate-carbohydrate beverage (PRO-CHO, 14 g protein/h and 69 g CHO/h) or an isocaloric carbohydrate beverage (CHO, 84 g/h) during each training session for six days (25-29 h cycling in total). Diet and training were standardized and supervised. The diet was energy balanced and contained 1.7 g protein/kg/day. A 10-s peak power test and a 5-min all-out performance test were conducted before and after the first training session and repeated at day 6 of the camp. Blood and saliva samples were collected in the morning after overnight fasting during the week and analyzed for biochemical markers of muscle damage, stress, and immune function. Results: In both groups, 5-min all-out performance was reduced after the first training session and at day 6 compared to before the first training session, with no difference between groups. Peak power in the sprint test did not change significantly between tests or between groups. In addition, changes in markers for muscle damage, stress, and immune function were not significantly influenced by treatment. Conclusions: Intake of protein combined with carbohydrate during cycling at a training camp for top cyclists did not result in marked performance benefits compared to intake of carbohydrates when a recovery drink containing adequate protein and carbohydrate was ingested immediately after each training session in both groups. These findings suggest that the addition of protein to a carbohydrate supplement consumed during exercise does not improve recovery or performance in elite cyclists despite high demands of daily exhaustive sessions during a one-week training camp.
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| 34. |
- Kaminska, M., et al.
(författare)
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Radiative cooling of hot C_n and C_nH^- molecules
- 2015
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Ingår i: Journal of Physics, Conference Series. - 1742-6588 .- 1742-6596. ; 635
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have measured the rates of neutrals produced from 10 keV C_n or C_nH (n=2, 4, 6, 8, and 10) ion beams stored in one of DESIREE's 14 K storage rings. For n=4, 6, and 8 we observe marked differences between C_n and CnH cooling rates as inverse internal conversion [cf. S. Martin et al (2013) Phys. Rev. Lett. 110, 063003] processes are effective for the C_n ions only. Knowledge of the cooling rates of these ions are important for estimates of their formation and destruction rates in cold interstellar environments.
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| 35. |
- Kono, Naoko, et al.
(författare)
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Electronic and vibrational radiative cooling of the small carbon clusters C4− and C6−
- 2018
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 98:6
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Tidskriftsartikel (refereegranskat)abstract
- Delayed electron detachment yields of C4− and C6− induced by photoexcitation in an electrostatic ion storage ring were measured as functions of excitation energies and laser firing times, allowing for a mapping of their radiative cooling in a wide energy range. The energy window concept and discrimination of one- and twophoton absorption are critical in understanding the obtained results. The experimentally obtained electronic and vibrational cooling rates were consistent with a simulation based on detailed-balance theory. The even-odd alternation of vibrational cooling rates, predicted from IR intensities, was also examined. We found that the larger anion cools faster, with no indication of an even-odd alternation.
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| 36. |
- Kono, N., et al.
(författare)
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Inverse internal conversion in C4- below the electron detachment threshold
- 2015
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Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 17:38, s. 24732-24737
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Tidskriftsartikel (refereegranskat)abstract
- Inverse internal conversion followed by recurrent fluorescence was observed as a fast decay (10 μs range) in the time profile of neutral yields from photo-excited C4- molecular ions. We also elucidated the contribution of such electronic radiative cooling to the C4- ions with internal energy far below the detachment threshold by an alternative novel approach, observing the laser wavelength and storage time dependence (ms range) of the total yield of the photo-induced neutrals.
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| 37. |
- Mamontov, Eugen, 1955, et al.
(författare)
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Associations and dissociations with time-dependent reaction coefficients in finite polymer mixtures: The model and analytical-numerical method for solution by successive approximations
- 2017
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Ingår i: Applied Mathematical Modelling. - : Elsevier BV. - 0307-904X. ; 51, s. 109-128
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Tidskriftsartikel (refereegranskat)abstract
- The work deals with the association and dissociation reactions with time-dependent coef- ficients in finite mixtures of polymers dispersed in fluid media with solid components. The polymers are regarded to be formed by identical units, polymer-forming units (PFUs) and, thus, present homopolymers. The model takes into account the porosity of the dispersion- medium/polymer-mixture system. The work derives the model for the reactions in the fi- nite mixtures. The model presents a non-autonomous quadratic finite ODE system in a time-independent hyperplane and is based on the conservation law for the total num- ber of PFUs. A variety of engineering applications of the derived finite-mixture model are discussed. The simplest case of the finite mixtures, i.e., the monomer-dimer mix- tures with time-independent reaction coefficients is completely analyzed. An analytical- numerical (AN) method of the successive-approximations (SA) type is proposed for solv- ing the derived model. The AN/SA method includes explicit analytical expressions for each of the approximations in terms of the preceding approximation. The method is exact in the dissociation-only case. The approximations are expected to converge if the association- reaction coefficients are not too large and the zeroth approximations are not very far from the solution. The AN/SA method comprises two sequences of the approximations. If the first one converges uniformly in the entire time axis, then the limit function is a steady- state (or “dynamic equilibrium”) solution of the non-autonomous quadratic ODE system. The second sequence presumes that the first sequence is convergent in the above men- tioned sense. The second sequence is intended for calculation of the solutions of initial- value problems for the above ODE system in a semi-infinite time interval. The main differ- ences from common computational methods are formulated. The AN/SA method is quan- titatively illustrated with a few examples of the settings in the aforementioned case of monomer-dimer mixtures, also in comparison with the explicit Euler method. The form of the AN/SA method allows especially efficient implementation on multi-processor/multicore personal computers with graphic processing units even if the dimension of the state space is large. The developed model and method form a constructive framework for analysis or design of polymer mixtures dispersed in fluid-solid media. An application to prospective manufacturing of spatially heterogeneous polymer products is noted. A few directions for future research are proposed as well.
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| 38. |
- Partanen, Lauri, et al.
(författare)
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Effect of Conformers on Free Energies of Atmospheric Complexes
- 2016
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 120:43, s. 8613-8624
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Tidskriftsartikel (refereegranskat)abstract
- In this article we show how to calculate free energies for atmospherically relevant complexes when multiple conformers and/or isomers are present. We explain why the thermal averaging methods used in several published works are incorrect. On the basis of our two sample cases, the sulfuric acid−pinic acid complex and the H2SO4)3(NH3)3(H2O)4 cluster, we provide numerical evidence that the use of these incorrect formulas can result in errors larger than 1 kcal/mol. We recommend that if vibrational frequencies and thus Gibbs free energies of the individual conformers are unavailable, one should not attempt to correct for the presence of multiple conformers and instead use only the global minimum conformers for both reactants and products. On the contrary, if the free energies for the conformers are calculated for both reactants and products, their effect can be accounted for by the statistical mechanical methods presented in this article.
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| 39. |
- Rahinov, Igor, et al.
(författare)
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Effect of a localized charge on the stability of Van der Waals clusters
- 2016
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Ingår i: European Physical Journal D : Atomic, Molecular and Optical Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 70:12
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Tidskriftsartikel (refereegranskat)abstract
- The stability of anionic (SF6)N clusters (in the range of N < 23), generated in a supersonic expansion ion source with electron impact ionization, was investigated by measuring their blackbody induced radiative dissociation (BIRD) rates in an electrostatic ion beam trap (EIBT) at room temperature. The lifetime traces of EIBT-stored clusters were subjected to “master equation analysis” and the activation energies, Ea, for the evaporation of a SF6 monomer were extracted. We find that the decay rates of (SF6)N anionic clusters are larger than those of cationic SF5+ (SF6)N−1 measured previously by the same method, and their corresponding activation energies to be smaller. These observations provide further insight into the effect of localized charge on cluster stability.
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| 40. |
- Shiromaru, H., et al.
(författare)
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Cooling dynamics of carbon cluster anions
- 2015
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 635
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Tidskriftsartikel (refereegranskat)abstract
- A series of ion storage experiments on small carbon cluster anions was conducted to understand size-dependent cooling processes. The laser-induced delayed electron detachment time profile show clear even/odd alternation due to the presence of the electronic cooling. The time evolution of the internal energy distribution was simulated for Cn- (n=4 to 7) with a common procedure taking vibrational and electronic cooling into account.
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| 41. |
- Stockett, M.H., et al.
(författare)
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Spontaneous decay of small copper cluster anions, Cu_N^-, N = 3 - 6
- 2015
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Ingår i: Journal of Physics, Conference Series. - 1742-6588 .- 1742-6596. ; 635
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have measured the spontaneous neutral particle emission from beams of copper cluster anions (Cu_N, N = 3 to 6) stored in an electrostatic storage ring. These experiments have show that multiple structural isomers may be present in the beam.
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| 42. |
- Sundén, Erika, 1970, et al.
(författare)
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Stabilities of protonated water-ammonia clusters
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:18
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Tidskriftsartikel (refereegranskat)abstract
- Branching ratios of water and ammonia evaporation have been measured for spontaneous evaporation from protonated mixed clusters H+(H2On(NH3)(m) in the size range 0 <= n <= 11 and 0 <= m <= 7. Mixed clusters evaporate water except for clusters containing six or more ammonia molecules, indicating the formation of a stable core of one ammonium ion surrounded by four ammonia molecules and a second shell consisting predominantly of water. We relate evaporative branching ratios to free energy differences between the products of competing channels and determine the free energy differences for clusters with up to seven ammonia molecules. Clusters containing up to five ammonia molecules show a very strong scaling of these free energy differences. Published by AIP Publishing.
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| 43. |
- Suzuki, R., et al.
(författare)
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Vibrational radiative cooling of isolated C4- and C6-
- 2017
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Ingår i: Journal of Physics: Conference Series. XXX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2017) 26 July to 1 August 2017, Cairns, Australia. - : IOP Publishing. - 1742-6588 .- 1742-6596.
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Konferensbidrag (refereegranskat)abstract
- We have observed the storage-time dependence of the laser-induced electron detachment yields for the linear carbon cluster anions C4- and C6− stored in an electrostatic ion storage ring (TMU E-ring) with several laser wavelengths. The electron detachment yield reflects the decrease of the internal energy of the stored ions. We succeeded in obtaining the time evolution of the excitation energy distribution below the first dipole-allowed electronic excited energy Eex for C4- and C6−, which was well consistent to the behavior explained by vibrational IR-radiative cooling.
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| 44. |
- Thomas, Richard D., et al.
(författare)
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DESIREE : Physics with cold stored ion beams
- 2015
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Ingår i: DR2013. - : EDP Sciences. ; 84, s. 01004-01004
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Konferensbidrag (refereegranskat)abstract
- Here we will briefly describe the commissioning of the Double ElectroStatic Ion Ring ExpEriment (DESIREE) facility at Stockholm University, Sweden. This device uses purely electrostatic focussing and deflection elements and allows ion beams of opposite charge to be confined under extreme high vacuum and cryogenic conditions in separate rings and then merged over a common straight section. This apparatus allows for studies of interactions between cations and anions at very low and well-defined centre-of-mass energies (down to a few meV) and at very low internal temperatures (down to a few K).
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| 45. |
- Yoshida, M., et al.
(författare)
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Detection of recurrent fluorescence photons emitted from C4
- 2017
-
Ingår i: International conference on photonic electronic and atomic collisions 2017, 26 jul - 1 aug, Queensland, Australia. Journal of Physics, Conference Series 875:102016. - : IOP Publishing. - 1742-6588 .- 1742-6596.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We detected recurrent fluorescence photons from vibrationally hot C4- ions stored in an electrostatic ion storage ring. By virtue of the mass-independent storage condition, various anions produced in the laser ablation ion source were simultaneously stored with their own velocities, and ionic species emitting photons were identified from the temporal profile of the detected photons. The fluorescence synchronized with revolution of C4- , through the bandpass filter for the known absorption band, were clearly observed.
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