| 1. |
- Fink, Reinhold, et al.
(författare)
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Specific production of very long-lived core-excited sulfur atoms by 2p(-1)sigma* excitation of the OCS molecule followed by ultrafast dissociation
- 2006
-
Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 39:12, s. L269-L275
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Tidskriftsartikel (refereegranskat)abstract
- A core-excited sulfur state with a lifetime almost one order of magnitude longer than in molecular 2p core-hole states is selectively produced by ultrafast dissociation of S 2p -> sigma* excited OCS. Clear evidence for this is provided by strong atomic peaks (20% of the total intensity) in x-ray fluorescence but very weak ones (2%) in the corresponding resonant Auger spectrum. Corroborating the assignment of the spectra, ab initio calculations explain the enhanced lifetime: the Auger decay of the produced D-3(3) (2p(5)3p(5)) sulfur state is strongly decreased as it contradicts a newly derived propensity rule of the L2,3MM Auger decay.
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| 2. |
- Månsson, Erik, et al.
(författare)
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Double ionization probed on the attosecond timescale
- 2014
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Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 10:3, s. 207-211
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Tidskriftsartikel (refereegranskat)abstract
- Double ionization following the absorption of a single photon is one of the most fundamental processes requiring interaction between electrons(1-3). Information about this interaction is usually obtained by detecting emitted particles without access to real-time dynamics. Here, attosecond light pulses(4,5), electron wave packet interferometry(6) and coincidence techniques(7) are combined to measure electron emission times in double ionization of xenon using single ionization as a clock, providing unique insight into the two-electron ejection mechanism. Access to many-particle dynamics in real time is of fundamental importance for understanding processes induced by electron correlation in atomic, molecular and more complex systems.
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| 3. |
- Bueno, AM, et al.
(författare)
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Influence of chemical bonds on the lifetime of the molecular-field-split 2p levels in H2S
- 2003
-
Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 67, s. 22714:1-7
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Tidskriftsartikel (refereegranskat)abstract
- Different lifetime broadenings in molecular-field-split 2p core levels in H2S are predicted theoretically and are identified in an experimental investigation of the S 2p Auger electron spectrum. The measurements were performed for the transition to the vibrationally resolved X(1)A(1) ground state of H2S2+. The lifetimes of the 3e(1/2) and 5e(1/2) levels of the 2p ionized molecule are found to be 64 and 74 meV, respectively. This unambiguous determination of the lifetime difference of 10+/-1 meV is only possible as the 4e(1/2)-->X(1)A(1)(2b(1)(-2)) decay channel that overlaps the 5e(1/2)-->X(1)A(1)(2b(1)(-2)) channel is practically suppressed in Auger decay in H2S. The lifetime difference is confirmed by ab initio calculations. A theoretical analysis shows that it results from the mutual orientation of the core hole in the intermediate states and the valence electron density in the sulfur 3p orbitals. Both are strongly influenced by the chemical bond. Thus the observed effect is the direct result of a fundamental property of molecular electronic structure.
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| 4. |
- Lindgren, Andreas, et al.
(författare)
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Core localization and sigma( *) delocalization in the O 1s core-excited sulfur dioxide molecule.
- 2008
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:11
-
Tidskriftsartikel (refereegranskat)abstract
- Electron-ion-ion coincidence measurements of sulfur dioxide at discrete resonances near the O 1s ionization edge are reported. The spectra are analyzed using a model based upon molecular symmetry and on the geometry of the molecule. We find clear evidence for molecular alignment that can be ascribed to symmetry properties of the ground and core-excited states. Configuration interaction (CI) calculations indicate geometry changes in accord with the measured spectra. For the SO(2) molecule, however, we find that the localized core hole does not produce measurable evidence for valence localization, since the transition dipole moment is not parallel to a breaking sigma(*) O-S bond, in contrast to the case of ozone. The dissociation behavior based upon the CI calculations using symmetry-broken orbitals while fixing a localized core-hole site is found to be nearly equivalent to that using symmetry-adapted orbitals. This implies that the core-localization effect is not strong enough to localize the sigma(*) valence orbital.
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| 5. |
- Mocellin, Alexandra, et al.
(författare)
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Site selective dissociation upon core ionization of ozone
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 435:4-6, s. 214-218
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Tidskriftsartikel (refereegranskat)abstract
- Ozone is found to exhibit substantial site-selective fragmentation when its fragment ions are collected in coincidence with energy selected electrons. We find a preferential production of the O-2(+)/O+(O+/O+) ion pair upon ionization of the terminal (central) oxygen Is electron. Depending on the hole localization, Auger rates are different towards the various final states of the dication, which would produce the observed different fragmentation pattern. We also observe however an increase O-2(+)/O+ production for when the terminal core-hole state is vibrationally excited. This shows the role of the nuclear motion before the Auger decay in the observed site-specific.
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| 6. |
- Adler, SS, et al.
(författare)
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Single electrons from heavy-flavor decays in p + p collisions at root s=200 GeV
- 2006
-
Ingår i: Physical Review Letters. - 1079-7114. ; 96:3
-
Tidskriftsartikel (refereegranskat)abstract
- The invariant differential cross section for inclusive electron production in p+p collisions at root s=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4 <= p(T) <= 5.0 GeV/c in the central rapidity region (vertical bar eta vertical bar <= 0.35). The contribution to the inclusive electron spectrum from semileptonic decays of hadrons carrying heavy flavor, i.e., charm quarks or, at high p(T), bottom quarks, is determined via three independent methods. The resulting electron spectrum from heavy-flavor decays is compared to recent leading and next-to-leading order perturbative QCD calculations. The total cross section of charm quark-antiquark pair production is determined to be sigma(c (c) over bar) = 0.92 +/- 0.15(stat) +/- 0.54(syst) mb.
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| 7. |
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| 8. |
- Andersen, J. N., et al.
(författare)
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Vibrational fine structure in the C 1s core level photoemission of chemisorbed molecules : Ethylene and ethylidyne on Rh(111)
- 1997
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Ingår i: Chemical Physics Letters. - 0009-2614. ; 269:3-4, s. 371-377
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Tidskriftsartikel (refereegranskat)abstract
- The origin of fine structure in the core-level photoemission spectra of the C2H4, C2D4, C2H3 and C2D3 molecules chemisorbed on Rh(111) is probed in a careful high-resolution study showing that this structure arises from internal molecular vibrations rather than from other chemically-shifted carbon atoms. It is shown by comparison of the adsorbate and gas-phase spectra that the underlying features are the same despite differences arising from adsorption. This new approach to the investigation of adsorbed molecules may prove to be useful in further studies of other systems and the possibility that such effects may exist could lead to the reinterpretation of other adsorbate systems.
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| 9. |
- Andersson, Tomas, et al.
(författare)
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Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy
- 2011
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:9, s. 094511-
-
Tidskriftsartikel (refereegranskat)abstract
- Plasmons are investigated in free nanoscale Na, Mg, and K metal clusters using synchrotron radiation-based x-ray photoelectron spectroscopy. The core levels for which the response from bulk and surface atoms can be resolved are probed over an extended binding energy range to include the plasmon loss features. In all species the features due to fundamental plasmons are identified, and in Na and K also those due to either the first order plasmon overtones or sequential plasmon excitation are observed. These features are discussed in view of earlier results for planar macroscopic samples and free clusters of the same materials.
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| 10. |
- Baev, A., et al.
(författare)
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Doppler interference in dissociative resonant photoemission
- 2002
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 66:2
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.
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| 11. |
- Baev, A., et al.
(författare)
-
Geometrical information on core-excited states obtained from interference quenching of vibrational states in resonant x-ray photoemission
- 2003
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 67:2
-
Tidskriftsartikel (refereegranskat)abstract
- An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X (2)Sigma(g)(+) final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.
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| 12. |
- Barillot, T., et al.
(författare)
-
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
-
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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| 13. |
- Barillot, T., et al.
(författare)
-
Attosecond time delays in C-60 valence photoemissions at the giant plasmon
- 2015
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 635, s. 112074-112074
-
Konferensbidrag (refereegranskat)abstract
- We perform time-dependent local density functional calculations of the time delay in C-60 HOMO and HOMO-1 photoionization at giant plasmon energies. A semiclassical model is used to develop further insights.
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| 14. |
- Burmeister, F., et al.
(författare)
-
A study of the inner-valence ionization region in HCl and DCl
- 2004
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 37:6, s. 1173-1183
-
Tidskriftsartikel (refereegranskat)abstract
- An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (similar to30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV.
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| 15. |
- Burmeister, Florian, et al.
(författare)
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Description and performance of an electron-ion coincidence TOF spectrometer used at the Brazilian synchrotron facility LNLS
- 2010
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 180:1-3, s. 6-13
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports the characteristics and performance of a Time-of-Flight Mass Spectrometer (TOF-MS) for coincidence measurements between electrons and ions that has been developed jointly in Sweden and Brazil. The spectrometer, used for studies of inner-shell photoexcitation of molecules in the gas-phase, has been optimized by implementing ion and electron lenses to allow the use of relatively small diameter detectors. Simulations were performed to understand the lens performance and they show that ions (electrons) could be collected without angular discrimination with a maximum kinetic energy up to ten (two) times higher than without the lens actions. A rotary vacuum chamber allows the spectrometer axis to be positioned at different angles relative to the polarization vector of the excitation beam. An important characteristic of the apparatus is that the acquisition setup allows a multi-hit capability with 1 ns resolution. Hereby, Photoelectron-Photoion-Photoion Coincidence (PEPIPICO) measurements can be performed on molecules containing two or more atoms of equal mass. A method to obtain experimental detection efficiencies of a single ion and one of one, two or three electrons has been developed. A systematic study of the interaction region has been performed to determine the shape of the photon and gas beams. Measurements on molecular nitrogen demonstrate the spectrometer's ability to resolve fragments with the same charge to mass ratio arriving within only a few ns. Simulations and experimental results of fragmentation of two singly charged cation nitrogen atoms agree, confirming that the spectrometer performance is well understood. (C) 2010 Elsevier B.V. All rights reserved.
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| 16. |
- Burmeister, F, et al.
(författare)
-
Nonadiabatic effects in photoelectron spectra of HCl and DCl. I. Experiment
- 2002
-
Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 65:1
-
Tidskriftsartikel (refereegranskat)abstract
- The HCl inner-valence photoelectron band at 26 eV binding energy has been recorded at high resolution. Discrete peaks arising from at least two separate vibrational progressions are superimposed on the broad continuum. Fano profiles are visible in one of the progressions. This indicates interference between superimposed electronic states, where weak avoided crossing allows two adiabatic states to couple. In the isotopic DCl molecular spectrum, the discrete lines are less pronounced, due to slower dissociation and therefore less coupling between the continuum and the bound state.
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| 17. |
- Bässler, M., et al.
(författare)
-
Beam line I411 at MAX II - Performance and first results
- 2001
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 469:3, s. 382-393
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the characteristics and first results from the soft X-ray beam line I411, based on an undulator at the third generation synchrotron facility MAX II, Sweden. The beam line is designed for high-resolution, angle-resolved electron spectroscopy on gases, liquids and solids. Main components are the modified SX700 monochromator and the end station, both of which were previously used at beam line 51 at MAX I. The end station is equipped with a rotatable SES-200 hemispherical electron-analyser. Before the end station, a one-metre section is reserved for exchangeable experimental set-ups. The usable photon energy range is 50-1500 eV and the photon flux is two orders of magnitudes higher compared to beam line 51. At 400 eV a resolving power of about 5700 in the first order of the monochromator grating could be obtained. In gas phase, a total electron energy resolution of 16 meV has been achieved. Detailed results on the undulator performance, flux, photon and electron energy resolution as well as some technical details are presented here. As an example of the capabilities of the beam line I411, we present the fully vibrationally resolved Auger resonant Raman electron spectrum of gas-phase N 2.
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| 18. |
- da Silva, DA, et al.
(författare)
-
Vibronic coupling in the ground and excited states of the naphthalene cation
- 2004
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :15, s. 1702-1703
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Tidskriftsartikel (refereegranskat)abstract
- The hole - vibrational coupling in naphthalene is studied using high-resolution gas-phase photoelectron spectroscopy and density functional theory calculations (DFT), and a remarkable increase of the coupling with low-frequency vibrations is observed in the excited states.
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| 19. |
- de Jong, Michel P, et al.
(författare)
-
Femtosecond charge transfer in assemblies of discotic liquid crystals
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:40, s. 15784-15790
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Tidskriftsartikel (refereegranskat)abstract
- The electronic coupling strength within columns of discotic liquid crystals is investigated using core-level resonant photoemission spectroscopy. Coexisting well-ordered and disordered regions are identified in thin films of tetra-alkoxy-substituted phthalocyanines with the aid of near edge X-ray absorption fine structure and photoelectron spectroscopies. These different regions are used to derive a lower limit for the intermolecular charge transfer bandwidth within the framework of the core-hole clock principle. We find average charge transfer times on the order of a few femtoseconds, that is, significantly faster than the C(ls) core-hole lifetime, which indicates a surprisingly strong electronic coupling between the phthalocyanine units as compared to what is expected from the charge transport characteristics of this material. © 2008 American Chemical Society.
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| 20. |
- de Jong, Michel P, 1970-, et al.
(författare)
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Orbital-specific dynamic charge transfer from Fe(II)-tetraphenylporphyrin molecules to molybdenum disulfide substrates
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:3, s. 35448-
-
Tidskriftsartikel (refereegranskat)abstract
- Orbital-specific femtosecond charge transfer dynamics between Fe(II)-tetraphenylporphyrin molecules and semimetallic molybdenum disulfide substrates is investigated using core-level resonant photoemission spectroscopy. The electronic coupling to the substrate and the efficiency of charge transport across the interface is found to be different for the individual molecular electronic subsystems. In particular, electrons excited at the phenyl substituents are transferred within 3–6 fs, while hopping from the porphyrin ring is slower than 30 fs.
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| 21. |
- Eland, John H. D., 1941, et al.
(författare)
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Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects
- 2014
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:18
-
Tidskriftsartikel (refereegranskat)abstract
- Multi-coincidence experiments with detection of both electrons and ions from decay of core-excited and core-ionized states of CO2 confirm that O-2(+) is formed specifically in Auger decay from the C1s-pi* and O1s-pi* resonances. Molecular rearrangement occurs by bending in the resonant states, and O-2(+) is produced by both single and double Auger decay. It is suggested that electron capture by C+ after partial dissociation in the doubly ionized core of excited CO2+, formed by shake-up in spectator resonant Auger decay, accounts for high kinetic energy and high internal energy in some C + O-2(+) fragments. (C) 2014 AIP Publishing LLC.
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| 22. |
- Eriksson, Mikael, et al.
(författare)
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Accelerators for synchrotron radiation
- 2005
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Ingår i: Electrostatic Accelerators: Fundamentals and Applications. - 1611-1052. ; , s. 36-50
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 23. |
- Feifel, R, et al.
(författare)
-
A quantitative analysis of the N 1s ->pi* photoabsorption profile in N-2: new spectroscopical constants for the core-excited state
- 2004
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 383:3-4, s. 222-229
-
Tidskriftsartikel (refereegranskat)abstract
- The N 1s --> pi* photoabsorption profile of N-2 is quantitatively analysed. New spectroscopical constants for the N 1s(-1) pi* core-excited state are determined from NEXAFS spectra and compared to previously published data. The accuracy of the new spectroscopical constants is discussed and error bars are given for the present data analysis. The goodness of the new spectroscopical constants is demonstrated by lifetime vibrational interference (LVI) simulations of the resonant Auger decay from the N 1s(-1) pi* core-excited state to the A(2)Pi(u) singly ionized final state of N-2. These new values give a much better agreement with recently obtained experimental data compared to the previously published ones.
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| 24. |
- Feifel, Raimund, et al.
(författare)
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From localised to delocalised electronic states in free Ar, Kr and Xe clusters
- 2004
-
Ingår i: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 30:3, s. 343-351
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Tidskriftsartikel (refereegranskat)abstract
- We present new results for the inner valence levels of clusters of the three inert gases Ar, Kr and Xe based on photoelectron spectroscopy studies. The inner valence levels are compared to the localised core levels and to the delocalised outer valence levels. This comparison shows a gradual change from a relatively localised behaviour for Ar inner valence 3s, over the intermediate case of Kr inner valence 4s, to a more delocalised behaviour for Xe inner valence 5s. This change correlates well with the ratio between the orbital sizes and the interatomic distances. The Kr4s intermediate case is found to exhibit characteristics of both localised and delocalised behaviour.
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| 25. |
- Feifel, Raimund, et al.
(författare)
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Generalization of the duration-time concept for interpreting state of the art high resolution resonant photoemission spectra
- 2004
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Ingår i: Physical Review A. ; 69
-
Tidskriftsartikel (refereegranskat)abstract
- The duration-time concept, vastly successful for interpreting the frequency dependence of resonant radiative and nonradiative x-ray scattering spectra, is tested for fine-scale features that can be obtained with state of the art high-resolution spectroscopy. For that purpose resonant photoelectron (RPE) spectra of the first three outermost singly ionized valence states X 2Σg+, A 2Πu, and B 2Σu+, are measured for selective excitations to different vibrational levels (up to n=13) of the N 1s→π* photoabsorption resonance in N2 and for negative photon frequency detuning relative to the adiabatic 0-0 transition of this resonance. It is found that different parts of the RPE spectrum converge to the spectral profile of direct photoionization (fast scattering) for different detunings, and that the RPE profiles are asymmetrical as a function of frequency detuning. The observed asymmetry contradicts the picture based on the simplified notation of a common scattering duration time, but is shown to agree with the here elaborated concept of partial and mean duration times. Results of the measurements and the simulations show that the duration time of the scattering process varies for different final electronic and different final vibrational states. This owes to two physical reasons: one is the competition between the fast “vertical” and the slow “resonant” scattering channels and the other is the slowing down of the scattering process near the zeros of the real part of the scattering amplitude.
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| 26. |
- Feifel, Raimund, et al.
(författare)
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"Hidden"" vibrations in CO: reinvestigation of resonant Auger decay for the C 1s to pi /sup */ excitation
- 2002
-
Ingår i: Physical Review A. ; 65:5, s. 52701-52701
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Tidskriftsartikel (refereegranskat)abstract
- We report an experimental investigation of higher vibrational levels (ν′>2) of the C 1s→π* excitation in CO utilizing resonant Auger electron spectroscopy. These vibrational states are not readily seen in a total yield absorption spectrum, whereas they are shown to be discernable in a partial electron yield spectrum. Furthermore, the nature of the spectator part between EBin=26.5 and 30 eV, being subject of an ongoing debate, is discussed on the grounds of the presented experimental data. The experiments indicate that the formally used adiabatic framework for the multitude of close lying 2Π potential curves is inappropriate, but that a diabatic treatment can be used for the interpretation of the spectra.
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| 27. |
- Feifel, R., et al.
(författare)
-
Interference quenching of nu('')=1 vibrational line in resonant photoemission of N-2 : A possibility to obtain geometrical information on the core-excited state
- 2002
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 89:10
-
Tidskriftsartikel (refereegranskat)abstract
- An interference quenching of the nu=1 vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the nu=1 and nu=0 vibrational levels of the X(2)Sigma(g)(+) final state shows a surprising nonmonotonous variation as a function of frequency detuning, going through a minimum with a complete suppression of nu=1. We have developed a simple model which shows a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance R-c(0) of the core-excited state. A new way is thus established of determining the equilibrium bond distance for the core-excited state with a precision deltaR(c)(0)<10(-3) Angstrom.
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| 28. |
- Feifel, R, et al.
(författare)
-
Probing doubly excited ionic states of N-2(+) via a triple excitation above the N 1s threshold in the N-2 molecule
- 2003
-
Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 67:3: 032504
-
Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved resonant Auger-electron spectroscopy has been carried out on the nitrogen molecule at selected photon energies around 419 eV, where a 1s core electron and two valence electrons are promoted into the lowest unoccupied molecular orbital 1pi(g). Significant enhancement of a specific band, which cannot be disentangled in direct photoionization, is observed at a binding energy of 37.6 eV, with a value of the anisotropy parameter beta much smaller than 2. We assign this new band to the transition to a doubly excited cationic state of N-2, in which two of the excited valence electrons remain in the 1pi(g) orbital, proposing a "double spectator" type decay mechanism. This observation shows how to preferentially probe multiply excited configurations of cations using multiple resonant excitation.
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| 29. |
- Feifel, Raimund, et al.
(författare)
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Probing the valence character of O-1s -> Rydberg excited O-2 by participator Auger decay measurements and partial ion yield spectroscopy following x-ray absorption
- 2007
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:17, s. 174304-
-
Tidskriftsartikel (refereegranskat)abstract
- The valence character of O 1s -> Rydberg excited O-2 is investigated by means of participator Auger decay spectroscopy, performed at selected photon energies across the K-shell resonance region, and by means of partial ion yield x-ray absorption spectroscopy. For several of the excitation energies studied, the authors find substantial sigma(*)((4)Sigma(-)(u),(2)Sigma(-)(u)) valence character being mixed with ns sigma and np sigma ((4)Sigma(-)(u),(2)Sigma(-)(u)) Rydberg states. An experimental indication of a coupling between the channels associated with quartet and doublet ion cores is considered and discussed. New spectroscopic constants are derived for the singly ionized X (2)Pi(g) state of O-2 based on the observation of at least 20 vibrational sublevels.
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| 30. |
- Feifel, R., et al.
(författare)
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Profile of resonant photoelectron spectra versus the spectral function width and photon frequency detuning
- 2004
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 70:3
-
Tidskriftsartikel (refereegranskat)abstract
- The outermost, singly ionized valence state of N-2, the X (2)Sigma(g)(+) state, is investigated in detail as a function of the photon frequency bandwidth for core excitation to the N 1s-->pi(*) resonance, where the photon frequency is tuned in between the first two vibrational levels of this bound intermediate electronic state. We find a strong, nontrivial dependence of the resulting resonant photoemission spectral profile on the monochromator function width and the frequency of its peak position. For narrow bandwidth excitation we observe a well resolved vibrational fine structure in the final electron spectrum, which for somewhat broader bandwidths gets smeared out into a continuous structure. For even broader monochromator bandwidths, it converts again into a well resolved vibrational progression. In addition, spectral features appearing below the adiabatic transition energy of the ground state of N-2(+) are observed for broadband excitation. A model taking into account the interplay of the partial scattering cross section with the spectral function is presented and applied to the X (2)Sigma(g)(+) final state of N-2(+).
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| 31. |
- Feifel, R., et al.
(författare)
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Role of stray light in the formation of high-resolution resonant photoelectron spectra : an experimental and theoretical study of N-2
- 2004
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 134:1, s. 49-65
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Tidskriftsartikel (refereegranskat)abstract
- We show that the undular stray light, diffusely scattered by the optical system of a synchrotron beamline, can play an important role in the formation of high-resolution resonant photoelectron (RPE) spectra. The influence of the stray light is mediated through the Stokes doubling effect, with the Lorentzian tail of the spectral function being replaced by a more complicated form. This effect is shown to appear in the high-resolution resonant photoelectron spectrum of the N-2 molecule in which the spectral shape of the non-Raman (NR) bands differs qualitatively for the A(2)Pi(u) and X(2)Sigma(g)(+) final states. A particularly large enhancement of the non-Raman Stokes line is observed for the A-state while the picture is inverted for the X-state where the non-Raman band is suppressed. It is shown that the resonant photoemission profile is affected by two qualitatively different detunings, the detuning of the monochromatized line relative to the photoabsorption line and the detuning of the undulator harmonic relative to the same reference line. The experimental data show that the relative intensity of the non-Raman line strongly depends on the tuning of the undulator harmonic with respect to the selected monochromator bandpass, leading to a strong decrease of the Stokes line intensity for certain undulator detunings. A clear red-shift asymmetry for the decrease in the Stokes line intensity is observed when the monochromator line is detuned towards negative photon frequencies, whereas the picture is reverted for the situation of a positively detuned monochromator line. The results show the necessity to control the stray light and to investigate both the Raman and non-Raman contributions to the spectral profiles in order to avoid misinterpretation and in order to make full use of the information available in resonant photoemission spectra of molecules.
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| 32. |
- Feifel, R., et al.
(författare)
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X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance : Experiment and theory
- 2008
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:6
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Tidskriftsartikel (refereegranskat)abstract
- We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.
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| 33. |
- Fink, RF, et al.
(författare)
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Spin-orbit selectivity observed for the HCl+ ((X)over-tilde (II)-I-2) state using resonant photoemission
- 2002
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 65:3
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Tidskriftsartikel (refereegranskat)abstract
- We report the experimental observation of a strongly selective population of the spin-orbit components in the HCl+ (X) over tilde (2)Pi(Omega) states after excitation into the dissociative 2p(-1)6sigma* core excited state. A progression of highly excited vibrational states with either the Omega=3/2 or Omega=1/2 component of the final state is populated, respectively, when the excitation is tuned in the 2p(3/2)(-1)6sigma*or2p(1/2)(-1)6 sigma* part of the resonance. This effect is explained theoretically to be due to the orientational selectivity of the excitation process and the preference of the L-2,L-3 VV Auger process to produce valence holes with the same orientation as the core holes.
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| 34. |
- Friedlein, Rainer, et al.
(författare)
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Electronic structure of conjugated polymers and interfaces in polymer-based electronics
- 2003
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Ingår i: Synthetic Metals (Proceedings of the International Conference on Science and Technology of Synthetic Metals). - 0379-6779. ; 135:1-3, s. 275-277
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Konferensbidrag (refereegranskat)abstract
- The electronic structure of conjugated polymers and interfaces in polymer-based electronics were analyzed. Fine structure were observed in the region of the first resonance with pi-final state symmetry, between 284.1 eV and 285.8 eV. The electronic transitions from the non-dispersed C(1s) level to specific parts of the unoccupied band structure were generated. It was found that for a dispersing valence band, in the presence of a core-hole, a given photon energy corresponded to an excitation into a state with a distinct wave vectors.
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| 35. |
- Friedlein, Rainer, et al.
(författare)
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Role of electronic localization and charge-vibrational coupling in resonant photoelectron spectra of polymers : Application to poly(para-phenylenevinylene)
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:12
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Tidskriftsartikel (refereegranskat)abstract
- A combination of x-ray absorption and resonant photoemission (RPE) spectroscopy has been used to study the electronic structure of the one-dimensional conjugated polymer poly (para-phenylenevinylene) in nonordered (as prepared) thin films. The dispersion of RPE features for the decay to localized and delocalized bands are qualitatively different. A theory for band dispersion of RPE in polymers is given, showing the important roles of electronic state localization and vibrational (phonon) excitations for the character of the dispersion.
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| 36. |
- Gisselbrecht, Mathieu, et al.
(författare)
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Charge migration and decay of doubly charged ammonia clusters
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:2, s. 022112-
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Tidskriftsartikel (refereegranskat)abstract
- The photo-fragmentation of ammonia molecular clusters ionized with soft x-rays is studied for photon energies near the N-1s threshold. The fragmentation is studied with a 3D momentum mass spectrometer to access the energy and angular correlations between fragments. By choosing the cluster sizes below or above the critical size of stable dication, we investigate the coulomb explosion dynamics and the interplay between charge delocalization and mobility of molecules in the clusters.
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| 37. |
- Gisselbrecht, Mathieu, et al.
(författare)
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Photon energy dependence of fragmentation of small argon clusters
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:19
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation of small argon clusters with size below ten atoms is reported. In this size range significant modifications from the electronic properties and geometry take place. When tuning the photon energy through the argon 2p edge, the fragmentation pattern is changed. Specifically, cation dimer production is enhanced at the 2p(3/2)-> 4s resonance, while above the 2p edge almost complete atomization is observed. In both cases, the widths of the peaks in the mass spectra indicate that a large amount of kinetic energy is imparted to the fragment due to the formation of multiply charged clusters. A model based on "Coulomb explosion"-charge separation, simply resulting in a complete atomization of the cluster with no dependence on the photon energy-is insufficient to explain the observed photofragmentation of small clusters.
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| 38. |
- Gisselbrecht, Mathieu, et al.
(författare)
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Size dependent fragmentation of argon clusters in the soft x-ray ionization regime.
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:4
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (N=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters (N>/=100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slower processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ("heat") dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.
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| 39. |
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| 40. |
- Hjelte, I, et al.
(författare)
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Evidence of ultra-fast dissociation in ammonia observed by resonant Auger electron spectroscopy
- 2003
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Ingår i: Chemical Physics Letters. - 0009-2614. ; 370:5-6, s. 781-788
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Tidskriftsartikel (refereegranskat)abstract
- We present evidence for ultra-fast dissociation of molecular ammonia when photo-excited to the Nls --> 4a(1) core-hole state. This finding is based on resonant Auger spectroscopical results as well as qualitative arguments concerning the photon energy dependence of the Auger structures. Calculations of the excited state potential based on the Z + l approximation were performed. Both the calculations and the measurements indicate that the most likely fragmentation pathway for the core excited ammonia molecules leads to NH2* and H fragments. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 41. |
- J Doherty, Walter, et al.
(författare)
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Selective hydrogen bond disruption in adenine monolayer films by reaction with water
- 2009
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 174:1-3, s. 107-109
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution X-ray photoelectron spectroscopy of two-dimensional films of adenine on a highly oriented pyrolitic graphite [0 0 0 1] surface reveal bonding changes induced by exposure to water. The hydrogen-bond interactions between adenine molecules were replaced by adenine-water hydrogen bonds in a stepwise pattern. This reaction destroyed the film network and changed the chemical state of the nitrogen sites. The reaction with water molecules affected both the donor and acceptor states of the oxygen atoms, as compared to those in water. (C) 2009 Elsevier B.V. All rights reserved.
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| 42. |
- Kitajima, M., et al.
(författare)
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Angle-resolved photoion yield and resonant Auger spectroscopy for the doubly excited Rydberg states above the C 1s threshold of CO
- 2008
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 78:3, s. 033422-
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Tidskriftsartikel (refereegranskat)abstract
- Doubly excited core-hole states of carbon monoxide in the photon energy region of 300-305 eV, i.e., directly above the C 1s ionization threshold, have been studied using both angle-resolved ion-yield and high-resolution resonant Auger spectroscopies. The leading configurations of the most prominent doubly excited Rydberg states are assigned by careful analysis of the ion-yield spectra and the final-state spectra to C 1s(-1) (5 sigma(-1)2 pi S-1=1) 3s sigma (v'=0,1,2), C 1s(-1) (5 sigma(-1)2 pi S-1=0) 3s sigma (v'=0,1,2), and C 1s(-1) (5 sigma(-1)2 pi S-1=1) 4s sigma (v'=0,1), which can only be populated via a conjugate shake-up process. Analysis of the resonant Auger spectra provides an assignment of several two-hole-one-electron (2h-1e) final states.
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| 43. |
- Kitajima, M., et al.
(författare)
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Doppler effect in resonant photoemission from SF6 : Correlation between doppler profile and auger emission anisotropy
- 2003
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 91:21
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Tidskriftsartikel (refereegranskat)abstract
- Fragmentation of the SF6 molecule upon F 1s excitation has been studied by resonant photoemission. The F atomiclike Auger line exhibits the characteristic Doppler profile that depends on the direction of the photoelectron momentum relative to the polarization vector of the radiation as well as on the photon energy. The measured Doppler profiles are analyzed by the model simulation that takes account of the anisotropy of the Auger emission in the molecular frame. The Auger anisotropy extracted from the data decreases with an increase in the F-SF5 internuclear distance.
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| 44. |
- Kivimäki, A, et al.
(författare)
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Resonant Auger spectroscopy of argon clusters at the 2p threshold
- 2005
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 71:3
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Tidskriftsartikel (refereegranskat)abstract
- Resonant Auger spectra of large argon clusters have been measured at the Ar 2p edge. The decay spectra can give some information on the states reached in photon absorption. For example, the observation of the 3p(4)4p final states indicates the occurrence of the 2p(3/2)-> 4p excitation in clusters, whereas in atoms this excitation is dipole forbidden. Also the 3p(4)3d final states are identified in the resonant Auger spectra. A peculiar finding is that the normal Auger transitions in bulk cluster atoms are observed below the 2p ionization thresholds. This is explained by the excitation of the 2p electrons into the conduction band, followed by a rapid delocalization of the electron.
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| 45. |
- Laksman, Joakim, et al.
(författare)
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Development and characterization of a multiple-coincidence ion-momentum imaging spectrometer.
- 2013
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 84:12
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Tidskriftsartikel (refereegranskat)abstract
- The design and performance of a high-resolution momentum-imaging spectrometer for ions which is optimized for experiments using synchrotron radiation is presented. High collection efficiency is achieved by a focusing electrostatic lens; a long drift tube improves mass resolution and a position-sensitive detector enables measurement of the transverse momentum of ions. The optimisation of the lens for particle momentum measurement at the highest resolution is described. We discuss the overall performance of the spectrometer and present examples demonstrating the momentum resolution for both kinetics and for angular measurements in molecular fragmentation for carbon monoxide and fullerenes. Examples are presented that confirm that complete space-time focussing is possible for a two-field three-dimensional imaging spectrometer.
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| 46. |
- Laksman, Joakim, et al.
(författare)
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Dynamics of proton migration and dissociation in core-excited ethyne probed by multiple ion momentum imaging
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:24, s. 1-244305
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Tidskriftsartikel (refereegranskat)abstract
- The study focuses on the rapid geometry change in ethyne, excited near the carbon 1s edge. Core excitation and ionization leads to population of dicationic states in ethyne. We study three competing dissociation pathways associated with deprotonation in the linear ethyne molecule, and two cases of rapid proton migration. We investigate the alignment of the molecule in the excited state, and find startling differences in these three cases. We present evidence for a strong anisotropy in the production of H+2 /C+2 fragments through a rapid deformation of the molecule to a dibridged conformation with the transition dipole moment parallel to the polarization of the exciting radiation.
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| 47. |
- Laksman, Joakim, et al.
(författare)
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Nuclear motion in carbonyl sulfide induced by resonant core electron excitation
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:14, s. 1-144314
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Tidskriftsartikel (refereegranskat)abstract
- The angular anisotropy for selected dissociation channels is measured at resonantly excited states of and symmetries at the C and O K-shell ionization edges of carbonyl sulfide. While the kinetic energy released in the reaction is mainly independent of the excitation energy, the angular anisotropy and momentum correlation clearly show deformation of the OCS molecule in the C1s−Pi state. The discovery of a two-body fragmentation channel SO+/C+ with a well defined angular anisotropy indicates the rapid formation of the CSO isomeric species.
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| 48. |
- Laksman, Joakim, et al.
(författare)
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Rapid bond rearrangement in core-excited molecular water.
- 2013
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:44, s. 19322-19329
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Tidskriftsartikel (refereegranskat)abstract
- The angular anisotropy of fragments created in the dissociation of core-electron excited water molecules is studied to probe the correlation between fragmentation channels, kinematics and molecular geometry. We present fragment kinetic measurements for water molecules where the inner-shell oxygen electron is excited to the unoccupied 4a1 and 2b2 valence molecular orbitals. The kinematics of individual fragmentation channels are measured using fully three-dimensional momentum imaging of fragments. The results show that the geometry of the molecule and the kinetic energy of fragments are strongly coupled in the atomisation process. In addition we identify a fragmentation process arising from bond rearrangement evidenced by the H2(+)-O(+) ion pair which is accessible for resonant excitation of the 1s electron. In all of the two-body fragmentation processes the dissociation takes place along the potential-energy surface, while atomisation reveals both dissociation along the potential surface and Coulomb explosion. The angular distribution of fragments suggests that the bond rearrangement is very rapid; likely on a sub 10 fs time scale.
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| 49. |
- Laksman, Joakim, et al.
(författare)
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Role of the Renner-Teller effect after core hole excitation in the dissociation dynamics of carbon dioxide dication.
- 2012
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:10
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation of the doubly-charged carbon dioxide molecule is studied after photoexcitation to the C 1s(1)2π(u) and O 1s(1)2π(u) states using a multicoincidence ion-imaging technique. The bent component of the Renner-Teller split states populated in the 1s→ π∗ resonant excitation at both the carbon and oxygen 1s ionization edges opens pathways to potential surfaces in highly bent geometries in the dication. Evidence for a complete deformation of the molecule is found in the coincident detection of C(+) and O(2) (+) ions. The distinct alignment of this fragmentation channel indicates rapid deformation and subsequent fragmentation. Investigation of the complete atomization dynamics in the dication leading to asymmetric charge separation shows that the primary dissociation mechanisms, sequential, concerted, and asynchronous concerted, are correlated to specific fragment kinetic energies. The study shows that the bond angle in fragmentation can extend below 20°.
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| 50. |
- Le Guen, K, et al.
(författare)
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Development of a four-element conical electron lens dedicated to high resolution Auger electron-ion(s) coincidence experiments
- 2002
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 73:11, s. 3885-3894
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Tidskriftsartikel (refereegranskat)abstract
- A four-element conical electron lens has been developed in view of its integration to a double toroidal electron energy analyzer (DTA) dedicated to Auger electron-ion coincidence measurements. The lens design, using electron trajectory numerical simulations, was entirely guided by the perspective of analyzing energetic electrons with high resolution in the multicoincidence regime. The design, construction, and experimental characterization stages of this electron optics system are described in this article. Emphasis is put on the importance of third generation synchrotron radiation sources when performing such multicoincidence experiments.
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