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| 2. |
- Sankari, Anna, et al.
(author)
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Non-radiative decay and fragmentation in water molecules after 1a1-14a1 excitation and core ionization studied by electron-energy-resolved electron–ion coincidence spectroscopy
- 2020
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:7
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Journal article (peer-reviewed)abstract
- In this paper, we examine decay and fragmentation of core-excited and core-ionized water molecules combining quantum chemical calculations and electron-energy-resolved electron–ion coincidence spectroscopy. The experimental technique allows us to connect electronic decay from core-excited states, electronic transitions between ionic states, and dissociation of the molecular ion. To this end, we calculate the minimum energy dissociation path of the core-excited molecule and the potential energy surfaces of the molecular ion. Our measurements highlight the role of ultra-fast nuclear motion in the 1a1-14a1 core-excited molecule in the production of fragment ions. OH+ fragments dominate for spectator Auger decay. Complete atomization after sequential fragmentation is also evident through detection of slow H+ fragments. Additional measurements of the non-resonant Auger decay of the core-ionized molecule (1a1-1) to the lower-energy dication states show that the formation of the OH+ + H+ ion pair dominates, whereas sequential fragmentation OH+ + H+ → O + H+ + H+ is observed for transitions to higher dication states, supporting previous theoretical investigations.
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| 3. |
- Chernenk, Kirill, et al.
(author)
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Performance and characterization of the FinEstBeAMS beamline at the MAX IV Laboratory
- 2021
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In: Journal of Synchrotron Radiation. - 0909-0495. ; 28, s. 1620-1630
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Journal article (peer-reviewed)abstract
- FinEstBeAMS (Finnish-Estonian Beamline for Atmospheric and Materials Sciences) is a multidisciplinary beamline constructed at the 1.5 GeV storage ring of the MAX IV synchrotron facility in Lund, Sweden. The beamline covers an extremely wide photon energy range, 4.5-1300 eV, by utilizing a single elliptically polarizing undulator as a radiation source and a single grazing-incidence plane grating monochromator to disperse the radiation. At photon energies below 70 eV the beamline operation relies on the use of optical and thin-film filters to remove higher-order components from the monochromated radiation. This paper discusses the performance of the beamline, examining such characteristics as the quality of the gratings, photon energy calibration, photon energy resolution, available photon flux, polarization quality and focal spot size.
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| 4. |
- Grizolli, Walan, et al.
(author)
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Multilayer based soft-x-ray polarimeter at MAX IV Laboratory.
- 2016
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In: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 87:2
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Journal article (peer-reviewed)abstract
- A high precision five rotation-axes polarimeter using transmission multilayers as polarizers and reflection multilayers as analyzers has been designed and manufactured. To cover the extreme ultraviolet regime, Mo/Si, Cr/C, Sc/Cr, and W/B4C multilayers for transmission and reflection have also been designed and produced. The polarimeter mechanics is supported on a hexapod to simplify the alignment relative to photon beam. The instrument is designed so that it can be easily transferred between different beamlines.
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| 5. |
- Grizolli, Walan, et al.
(author)
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Use of astigmatic re-focusing at HP-XPS end-station
- 2013
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In: 11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012). - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 425
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Conference paper (peer-reviewed)abstract
- In this paper we present the refocusing optics for the new high pressure photoelectron spectroscopy (HP-XPS) branch line at MAX-lab, based on a plane grating monochromator with vertically collimated beam. For the HP-XPS instrument, the required spot size is dictated by the small geometric acceptance of the HP-XPS electron energy analyzer. Whereas a pair of bendable mirrors in a KB configuration has some advantages as refocusing elements, we have studied whether similar performance can be achieved with a single non-bendable mirror. In this solution, however, the need for strong horizontal magnification results in a strong vertical magnification and into a very asymmetric image, the height being just a fraction of the width. We have studied through an analytical geometrical model and ray tracing simulations the use of astigmatism to increase the vertical beam size up to the geometric acceptance of the detector. As a result the vertical beam size at sample plane is mostly determined by the photon angular distribution and is not dependent on the exit slit aperture size. In addition the vertical beam size can be controlled by the grating c(ff) parameter, making possible to adjust the photon density and minimize sample damage by the radiation.
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| 6. |
- Kivimaeki, A., et al.
(author)
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On the production of N-2(+) ions at the N 1s edge of the nitrogen molecule
- 2013
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In: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 87:6
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Journal article (peer-reviewed)abstract
- The N-2(+) ion yield of the N-2 molecule has been measured at the N 1s -> Rydberg excitations. It displays Fano-type line shapes due to interference between direct outer-valence photoionization and participator decay of the core-excited Rydberg states. The N-2(+) ion yield is compared with the total intensity of the outer-valence photoelectron lines obtained recently with electron spectroscopy (Kivimaki et al 2012 Phys. Rev. A 86 012516). The increasing difference between the two curves at the higher core-to-Rydberg excitations is most likely due to soft x-ray emission processes that are followed by autoionization. The results also suggest that resonant Auger decay from the core-valence doubly excited states contributes to the N-2(+) ion yield at the photon energies that are located on both sides of the N 1s ionization limit.
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| 7. |
- Kivimaeki, A., et al.
(author)
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Valence photoionization of the N-2 molecule in the region of the N 1s -> Rydberg excitations
- 2012
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 86:1
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Journal article (peer-reviewed)abstract
- The intensities of the X and A valence photoelectron lines of N-2 have been found to display Fano line shapes as a function of photon energy around the N 1s -> Rydberg excitations. The vibrational intensity distributions of these photoelectron lines change at the N 1s -> 3s sigma and 3p pi resonances. These effects indicate interference between direct and resonant photoionization channels. Our numerical simulations reproduce quite well the experimental results.
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| 8. |
- Kivimäki, Antti, et al.
(author)
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Fragmentation of Methanol Molecules after Core Excitation and Core Ionization Studied by Negative-Ion/Positive-Ion Coincidence Experiments
- 2018
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 122:1, s. 224-233
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Journal article (peer-reviewed)abstract
- We have studied the fragmentation of the methanol molecule after core excitation and core ionization by observing coincidences between negative and positive ions. Five different negative ions – H-, C-, CH-, O-, and OH- – were observed at both the C 1s and O 1s edges. As negative ion formation occurs after resonant and normal Auger decay of core-hole states, it is necessarily linked with the release of positively charged fragments. Our data show that such fragmentation can happen in many different ways: We found approximately 30 negative-ion/positive-ion/positive-ion coincidence (NIPIPICO) channels. All involve only singly charged positive ions. Fragmentation channels leading to atomic ions are the most probable, but positive molecular ions are also frequently found in the context of anion formation. Coincidence yields as a function of photon energy were determined for the most intense NIPIPICO channels. Adding together the data measured at different photon energies, we could also verify the occurrence of four-ion coincidences, which involved one negative ion (H- or O-) and three positive ions.
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| 9. |
- Kivimäki, Antti, et al.
(author)
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Negative-ion/positive-ion coincidence spectroscopy as a tool to identify anionic fragments : The case of core-excited CHF3
- 2020
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In: Journal of Mass Spectrometry. - : Wiley. - 1076-5174 .- 1096-9888. ; 55:5
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Journal article (peer-reviewed)abstract
- We have studied the dissociation of the trifluoromethane molecule, CHF3, into negative ionic fragments at the C 1s and F 1s edges. The measurements were performed by detecting coincidences between negative and positive ions. We observed five different negative ions: F−, H−, C−, CF−, and F2 −. Their production was confirmed by the analysis of triple coincidence events (negative-ion/positive-ion/positive-ion or NIPIPI coincidences) that were recorded with cleaner signals than those of the negative-ion/positive-ion coincidences. The intensities of the most intense NIPIPI coincidence channels were recorded as a function of photon energy across the C 1s and F 1s excitations and ionization thresholds. We also observed dissociation channels involving the formation of one negative ion and three positive ions. Our results demonstrate that negative-ion/positive-ion coincidence spectroscopy is a very sensitive method to observe anions, which at inner-shell edges are up to three orders of magnitude less probable dissociation products than cations.
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| 10. |
- Kokkonen, Esko, et al.
(author)
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Upgrade of the SPECIES beamline at the MAX IV Laboratory
- 2021
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In: Journal of Synchrotron Radiation. - 1600-5775. ; 28, s. 588-601
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Journal article (peer-reviewed)abstract
- The SPECIES beamline has been transferred to the new 1.5 GeV storage ring at the MAX IV Laboratory. Several improvements have been made to the beamline and its endstations during the transfer. Together the Ambient Pressure X-ray Photoelectron Spectroscopy and Resonant Inelastic X-ray Scattering endstations are capable of conducting photoelectron spectroscopy in elevated pressure regimes with enhanced time-resolution and flux and X-ray scattering experiments with improved resolution and flux. Both endstations offer a unique capability for experiments at low photon energies in the vacuum ultraviolet and soft X-ray range. In this paper, the upgrades on the endstations and current performance of the beamline are reported.
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