| 1. |
- Jahnke, T., et al.
(författare)
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Inner-Shell-Ionization-Induced Femtosecond Structural Dynamics of Water Molecules Imaged at an X-Ray Free-Electron Laser
- 2021
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Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- The ultrafast structural dynamics of water following inner-shell ionization is a crucial issue in high-energy radiation chemistry. We have exposed isolated water molecules to a short x-ray pulse from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we can image dissociation dynamics of individual molecules in unprecedented detail. We reveal significant molecular structural dynamics in H2O2+, such as asymmetric deformation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. We thus reconstruct several snapshots of structural dynamics at different time intervals, which highlight dynamical patterns that are relevant as initiating steps of subsequent radiation-damage processes.
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| 2. |
- Pathak, S., et al.
(författare)
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Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening
- 2020
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Ingår i: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4330 .- 1755-4349. ; 12:9, s. 795-800
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Tidskriftsartikel (refereegranskat)abstract
- Photoinduced isomerization reactions lie at the heart of many chemical processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics occurring on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free-electron laser to trace the ultrafast ring opening of gas-phase thiophenone molecules following ultraviolet photoexcitation. When combined with ab initio electronic structure and molecular dynamics calculations of the excited- and ground-state molecules, the results provide insights into both the electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state are shown to be driven by ballistic S-C bond extension and to be complete within 350 fs. Theory and experiment also enable visualization of the rich ground-state dynamics that involve the formation of, and interconversion between, ring-opened isomers and the cyclic structure, as well as fragmentation over much longer timescales.
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| 3. |
- Bolognesi, P., et al.
(författare)
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A study of the dynamical energy flow in uracil
- 2015
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635
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Tidskriftsartikel (refereegranskat)abstract
- The time resolved photoionization of C 1s in uracil following excitation of the neutral molecule by 260 nm pulses has been studied at LCLS.
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| 4. |
- Berrah, N., et al.
(författare)
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Femtosecond-resolved observation of the fragmentation of buckminsterfullerene following X-ray multiphoton ionization
- 2019
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 15, s. 1279-1283
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers have, over the past decade, opened up the possibility of understanding the ultrafast response of matter to intense X-ray pulses. In earlier research on atoms and small molecules, new aspects of this response were uncovered, such as rapid sequences of inner-shell photoionization and Auger ionization. Here, we studied a larger molecule, buckminsterfullerene (C60), exposed to 640eV X-rays, and examined the role of chemical effects, such as chemical bonds and charge transfer, on the fragmentation following multiple ionization of the molecule. To provide time resolution, we performed femtosecond-resolved X-ray pump/X-ray probe measurements, which were accompanied by advanced simulations. The simulations and experiment reveal that despite substantial ionization induced by the ultrashort (20fs) X-ray pump pulse, the fragmentation of C60 is considerably delayed. This work uncovers the persistence of the molecular structure of C60, which hinders fragmentation over a timescale of hundreds of femtoseconds. Furthermore, we demonstrate that a substantial fraction of the ejected fragments are neutral carbon atoms. These findings provide insights into X-ray free-electron laser-induced radiation damage in large molecules, including biomolecules.
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| 5. |
- Fang, L., et al.
(författare)
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Multiple Ionization and Double Core-hole Production in Molecules using the LCLS X-ray FEL
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:3, s. 032028-
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Tidskriftsartikel (refereegranskat)abstract
- We used the world's first hard x-ray FEL to investigate the response of molecular systems to the ultra-intense, femtosecond x-ray radiation. We report sequential multiphoton ionization, frustrated absorption and double core hole production mechanisms.
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| 6. |
- G. Öhrwall, M. Tchaplyguine, M. Gisselbrecht, M. Lundwall, R. Feifel, T. Rander, J. Schulz, R. R. T. Marinho, A. Lindgren, S. L. Sorensen, S. Svensson and O. Björneholm
(författare)
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Observation of elastic scattering effects on photoelectron angular distributions in free Xe clusters
- 2003
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Ingår i: J. Phys. B: At. Mol. Opt. Phys. ; :36, s. 3937-
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Guillemin, R., et al.
(författare)
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Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser
- 2023
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Ingår i: STRUCTURAL DYNAMICS-US. - 2329-7778. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H2O2+, D2O2+, and HDO2+, such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.
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| 8. |
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| 9. |
- Makos, I., et al.
(författare)
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Attosecond photoelectron spectroscopy using high-harmonic generation and seeded free-electron lasers
- 2023
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Ingår i: 2023 Photonics North, PN 2023. - 9798350326734
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Konferensbidrag (refereegranskat)abstract
- In this work, we use attosecond time-resolved techniques to investigate photoionization dynamics on its natural timescale, employing both high harmonic generation and seeded free-electron lasers to generate extreme ultraviolet attosecond pulse trains for our studies. With the former approach, we examine the role of nuclear motion in molecular photoionization dynamics, while with the latter we introduce a novel attosecond timing tool for single-shot characterization of the relative phase between the XUV and the infrared field.
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| 10. |
- Saleacuten, P., et al.
(författare)
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X-ray FEL-induced Double Core-Hole Formation in Polyatomic Molecules
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:2, s. 022083-
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Tidskriftsartikel (refereegranskat)abstract
- We use extremely intense, ultrashort soft X-Ray pulses generated by the LCLS X-Ray Free Electron Laser to investigate the production of molecular double core-hole states by sequential two-photon X-Ray absorption. The effect of critical LCLS parameters such as the number of photons per pulse, the pulse duration, and the focal spot size on the photoelectron and Auger spectra is modeled in detail and the results of these simulations are used as an aid in the interpretation of the experimental spectra obtained. The emphasis is on double core-hole formation in small polyatomic molecules such as CO2.
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| 11. |
- Sanchez-Gonzalez, A., et al.
(författare)
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Accurate prediction of X-ray pulse properties from a free-electron laser using machine learning
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Free-electron lasers providing ultra-short high-brightness pulses of X-ray radiation have great potential for a wide impact on science, and are a critical element for unravelling the structural dynamics of matter. To fully harness this potential, we must accurately know the X-ray properties: intensity, spectrum and temporal profile. Owing to the inherent fluctuations in free-electron lasers, this mandates a full characterization of the properties for each and every pulse. While diagnostics of these properties exist, they are often invasive and many cannot operate at a high-repetition rate. Here, we present a technique for circumventing this limitation. Employing a machine learning strategy, we can accurately predict X-ray properties for every shot using only parameters that are easily recorded at high-repetition rate, by training a model on a small set of fully diagnosed pulses. This opens the door to fully realizing the promise of next-generation high-repetition rate X-ray lasers.
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| 12. |
- Sanchez-Gonzalez, A., et al.
(författare)
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Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL
- 2015
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Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:23
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Tidskriftsartikel (refereegranskat)abstract
- We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.
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| 13. |
- Squibb, Richard J., et al.
(författare)
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Acetylacetone photodynamics at a seeded free-electron laser
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Thefirst steps in photochemical processes, such as photosynthesis or animal vision, involvechanges in electronic and geometric structure on extremely short time scales. Time-resolvedphotoelectron spectroscopy is a natural way to measure such changes, but has been hinderedhitherto by limitations of available pulsed light sources in the vacuum-ultraviolet and soft X-ray spectral region, which have insufficient resolution in time and energy simultaneously. Theunique combination of intensity, energy resolution, and femtosecond pulse duration of theFERMI-seeded free-electron laser can now provide exceptionally detailed information onphotoexcitation–deexcitation and fragmentation in pump-probe experiments on the 50-femtosecond time scale. For the prototypical system acetylacetone we report here electronspectra measured as a function of time delay with enough spectral and time resolution tofollow several photoexcited species through well-characterized individual steps, interpretedusing state-of-the-art static and dynamics calculations. These results open the way forinvestigations of photochemical processes in unprecedented detail.
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| 14. |
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| 15. |
- Asmussen, J. D., et al.
(författare)
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Unravelling the full relaxation dynamics of superexcited helium nanodroplets
- 2021
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:28, s. 15138-15149
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Tidskriftsartikel (refereegranskat)abstract
- The relaxation dynamics of superexcited superfluid He nanodroplets is thoroughly investigated by means of extreme-ultraviolet (XUV) femtosecond electron and ion spectroscopy complemented by time-dependent density functional theory (TDDFT). Three main paths leading to the emission of electrons and ions are identified: droplet autoionization, pump-probe photoionization, and autoionization induced by re-excitation of droplets relaxing into levels below the droplet ionization threshold. The most abundant product ions are He-2(+), generated by droplet autoionization and by photoionization of droplet-bound excited He atoms. He+ appear with some pump-probe delay as a result of the ejection He atoms in their lowest excited states from the droplets. The state-resolved time-dependent photoelectron spectra reveal that intermediate excited states of the droplets are populated in the course of the relaxation, terminating in the lowest-lying metastable singlet and triplet He atomic states. The slightly faster relaxation of the triplet state compared to the singlet state is in agreement with the simulation showing faster formation of a bubble around a He atom in the triplet state.
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| 16. |
- Bassler, M, et al.
(författare)
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Beam line 1411 at MAX II - performance and first results
- 2001
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Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT. - : ELSEVIER SCIENCE BV. - 0168-9002. ; 469:3, s. 382-393
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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 o
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| 17. |
- Bassler, M, et al.
(författare)
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Soft X-ray undulator beam line I411 at MAX-II for gases, liquids and solid samples
- 1999
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Ingår i: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA. - : ELSEVIER SCIENCE BV. - 0368-2048. ; 103, s. 953-957
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We report on the build-up of the new undulator beam line I411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were
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| 18. |
- 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
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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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| 19. |
- Bässler, M., et al.
(författare)
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Beam line I411 at MAX II - Performance and first results
- 2001
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - 0168-9002. ; 469:3, s. 382-393
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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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| 20. |
- Bässler, M., et al.
(författare)
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Soft x-ray undulator beam line 1411 at MAX-II for gases, liquids and solid samples
- 1999
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 101-103, s. 953-957
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Tidskriftsartikel (refereegranskat)abstract
- We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers.
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| 21. |
- Eland, John H. D., et al.
(författare)
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Single and multiple photoionisation of H(2)S by 40-250 eV photons
- 2011
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:41, s. 18428-18435
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Tidskriftsartikel (refereegranskat)abstract
- Multi-electron coincidence measurements on photoionisation of H(2)S have been carried out at photon energies from 40 to 250 eV. They quantify molecular field effects on the Auger process in detail and are in good agreement with the existing theory. Spectra of core-valence double ionisation of H(2)S are presented and partially analysed. Auger decays from the core-valence states produce triply charged product spectra with unexplained and surprising intensity distributions. Triple ionisation by the double Auger process from 2p hole states shows little effect of the molecular field splitting, but includes a substantial contribution from cascade processes, some involving dissociation in intermediate states. The onset of triple ionisation at the molecular geometry is determined as 61 +/- 0.5 eV.
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| 22. |
- Farrell, J. P., et al.
(författare)
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Ultrafast X-ray probe of nucleobase photoprotection
- 2012
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Ingår i: Quantum Electronics and Laser Science Conference. - 9781467318396 ; , s. 6327153-
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Konferensbidrag (refereegranskat)abstract
- We will present first results of a UV-pump X-ray-probe study of the photoprotection mechanism of thymine. The experiment used element specific Auger spectroscopy and was carried out at the LCLS.
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| 23. |
- Feifel, Raimund, et al.
(författare)
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Cationic double K-hole pre-edge states of CS2 and SF6
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in X-ray instrumentation have made it possible to measure the spectra of an essentially unexplored class of electronic states associated with double inner-shell vacancies. Using the technique of single electron spectroscopy, spectra of states in CS2 and SF6 with a double hole in the K-shell and one electron exited to a normally unoccupied orbital have been obtained. The spectra are interpreted with the aid of a high-level theoretical model giving excellent agreement with the experiment. The results shed new light on the important distinction between direct and conjugate shake-up in a molecular context. In particular, systematic similarities and di erences between pre-edge states near single core holes investigated in X-ray absorption spectra and the corresponding states near double core holes studied here are brought out.
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| 24. |
- Feifel, R., et al.
(författare)
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"Hidden" vibrations in CO : Reinvestigation of resonant Auger decay for the C 1s → π* excitation
- 2002
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947. ; 65:5 A, s. 527011-527018
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Tidskriftsartikel (refereegranskat)abstract
- The higher vibrational levels of the C 1s→π* excitation in carbon monooxide (CO) were investigated by using resonant Auger electron spectroscopy. The absorption profile of the CO was recorded in the partial electron yield mode. The results showed that the vibrational states were not seen in a total yield absorption spectrum whereas they were shown to be discernable in a partial electron yield spectrum.
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| 25. |
- 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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