| 1. |
- Bao, Zhuo, 1977-
(författare)
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Synchrotron Radiation Studies of Free and Adsorbed Molecules
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contains two parts. The first part concerns the research work on free molecules using synchrotron-radiation-related techniques. Auger electron spectra of two free open-shell molecules, O2 and NO, were studied experimentally and theoretically. Photoionization experimental technique with tunable synchrotron radiation source was used to induce core-level electron ionization and obtain the KVV normal Auger electron spectra. A quantitative assignment of O2 normal Auger spectrum was obtained by applying ab initio CI calculations and LVI Auger line shape simulations including the bond length dependence of Auger transition rates. The photon energy dependence of normal Auger electron spectra was focused on with photon energies in the vicinities of core-ionization threshold energies. Consequently, the MAPCI (Molecular Auger Post Collision Interaction) theory was developed. Taking the near-threshold O2 normal Auger spectrum as an example, the two extreme cases of MAPCI effect, “atomic-like PCI” and “molecular PCI”, were discovered and discussed. The effect of shape resonance on near-threshold molecular normal Auger spectrum was discussed taking NO near threshold normal Auger spectra as example.The second part deals with research work on the chemisorption of small epoxy organic molecules, ethylene oxide, methyl oxirane, on Si (100) surfaces. Synchrotron radiation related techniques, UPS, XPS and NEXAFS, were applied. Based on the valence photoemission spectra, C 1s and Si 2p XPS spectra, the epoxy ring opening reactions of these molecules in chemisorption process were proved. Further tentative search for the surface-adsorbate CDAD effect was performed, and no evident circular dichroism was confirmed.
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| 2. |
- Berholts, Marta, et al.
(författare)
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Photofragmentation of gas-phase acetic acid and acetamide clusters in the vacuum ultraviolet region
- 2017
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 147:19
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation of gas-phase acetamide and acetic acid clusters produced by a supersonic expansion source has been studied using time-of-flight mass spectrometry and the partial ion yield (PIY) technique combined with tunable vacuum-ultraviolet synchrotron radiation. Appearance energies of the clusters and their fragments were experimentally determined from the PIY measurements. The effect of clusterization conditions on the formation and fragmentation of acetic acid clusters was investigated. Ab initio quantum mechanical calculations were performed on both samples' dimers to find their neutral and ionized geometries as well as proton transfer energy barriers leading to the optimal geometries. In the case of the acetamide dimer, the reaction resulting in the production of ammoniated acetamide was probed, and the geometry of the obtained ion was calculated.
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| 3. |
- Berrah, Nora, et al.
(författare)
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Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:41, s. 16912-16915
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Tidskriftsartikel (refereegranskat)abstract
- Theory predicts that double-core-hole (DCH) spectroscopy can provide a new powerful means of differentiating between similar chemical systems with a sensitivity not hitherto possible. Although DCH ionization on a single site in molecules was recently measured with double-and single-photon absorption, double-core holes with single vacancies on two different sites, allowing unambiguous chemical analysis, have remained elusive. Here we report that direct observation of double-core holes with single vacancies on two different sites produced via sequential two-photon absorption, using short, intense X-ray pulses from the Linac Coherent Light Source free-electron laser and compare it with theoretical modeling. The observation of DCH states, which exhibit a unique signature, and agreement with theory proves the feasibility of the method. Our findings exploit the ultrashort pulse duration of the free-electron laser to eject two core electrons on a time scale comparable to that of Auger decay and demonstrate possible future X-ray control of physical inner-shell processes.
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| 4. |
- Carniato, Stéphane, et al.
(författare)
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N-K near edge x-ray absorption fine structures of acetonitrile in gas phase
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:21, s. 214301-
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic processes of N(1s) core-hole excitation in gas-phase CH3CN molecule have been studied at both Hartree-Fock and hybrid density-functional theory levels. The vibrational structure is analyzed for fully optimized core-excited states. Frank-Condon factors are obtained using the linear coupling model for various potential surfaces. It is found that the vibrational profile of the N-K absorption can be largely described by a summation of two vibrational progressions: a structure-rich profile of nu((CN)) stretching mode and a large envelope of congestioned vibrational levels related to the strong (-C-CN) terminal bending bond. Excellent agreement between theoretical and experimental spectra is obtained.
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| 5. |
- Chernenk, Kirill, et al.
(författare)
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Performance and characterization of the FinEstBeAMS beamline at the MAX IV Laboratory
- 2021
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 28, s. 1620-1630
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Fukuzawa, Hironobu, et al.
(författare)
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Real-time observation of X-ray-induced intramolecular and interatomic electronic decay in CH2I2
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- The increasing availability of X-ray free-electron lasers (XFELs) has catalyzed the development of single-object structural determination and of structural dynamics tracking in real-time. Disentangling the molecular-level reactions triggered by the interaction with an XFEL pulse is a fundamental step towards developing such applications. Here we report real-time observations of XFEL-induced electronic decay via short-lived transient electronic states in the diiodomethane molecule, using a femtosecond near-infrared probe laser. We determine the lifetimes of the transient states populated during the XFEL-induced Auger cascades and find that multiply charged iodine ions are issued from short-lived (∼20 fs) transient states, whereas the singly charged ones originate from significantly longer-lived states (∼100 fs). We identify the mechanisms behind these different time scales: contrary to the short-lived transient states which relax by molecular Auger decay, the long-lived ones decay by an interatomic Coulombic decay between two iodine atoms, during the molecular fragmentation. © 2019, The Author(s).
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| 7. |
- Itala, Eero, et al.
(författare)
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Gas-phase study on uridine : Conformation and X-ray photofragmentation
- 2015
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 142:19
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Tidskriftsartikel (refereegranskat)abstract
- Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. The measurements by combined electron and ion spectroscopy have been performed in gas phase utilizing synchrotron radiation. As uridine is a combination of d-ribose and uracil, which have been studied earlier with the same method, this study also considers the effect of chemical environment and the relevant functional groups. Furthermore, since in core ionization the initial core hole is always highly localized, charge migration prior to fragmentation has been studied here. This study also demonstrates the destructive nature of core ionization as in most cases the C 1s ionization of uridine leads to concerted explosions producing only small fragments with masses <= 43 amu. In addition to fragmentation patterns, we found out that upon evaporation the sugar part of the uridine molecule attains hexagonal form.
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| 8. |
- Itala, Eero, et al.
(författare)
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Photofragmentation of Serine Following C 1s Core Ionization-Comparison with Cysteine
- 2016
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 120:28, s. 5419-5426
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation pathways of doubly ionized serine molecules are investigated and compared with those of cysteine. The main motivation for the study is to investigate if an atomic substitution within the same group of elements, namely, replacing sulfur (in cysteine) with oxygen (in serine), causes a major change in the C 1s core ionization induced dissociation pattern in the molecules of an otherwise identical structure. The results show that in serine there is a single completely dominant fragmentation channel producing the (CNH2-4+, COH1-3+) pairs, whereas in cysteine there are also many other fragmentation channels. The employed experimental method was the photoelectron-photoion-photoion coincidence (PEPIPICO) technique combined with synchrotron radiation tuned to ionize desired core levels. Molecular dynamics calculations were also carried out in order to extract information on the fragmentation and the neutral final fragments.
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| 9. |
- Kooser, Kuno, et al.
(författare)
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Gas-phase endstation of electron, ion and coincidence spectroscopies for diluted samples at the FinEstBeAMS beamline of the MAX IV 1.5 GeV storage ring
- 2020
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 27, s. 1080-1091
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Tidskriftsartikel (refereegranskat)abstract
- Since spring 2019 an experimental setup consisting of an electron spectrometer and an ion time-of-flight mass spectrometer for diluted samples has been available for users at the FinEstBeAMS beamline of the MAX IV Laboratory in Lund, Sweden. The setup enables users to study the interaction of atoms, molecules, (molecular) microclusters and nanoparticles with short-wavelength (vacuum ultraviolet and X-ray) synchrotron radiation and to follow the electron and nuclear dynamics induced by this interaction. Test measurements of N2 and thiophene (C4H4S) molecules have demonstrated that the setup can be used for many-particle coincidence spectroscopy. The measurements of the Ar 3p photoelectron spectra by linear horizontal and vertical polarization show that angle-resolved experiments can also be performed. The possibility to compare the electron spectroscopic results of diluted samples with solid targets in the case of Co2O3 and Fe2O3 at the Co and Fe L 2,3-absorption edges in the same experimental session is also demonstrated. Because the photon energy range of the FinEstBeAMS beamline extends from 4.4 eV up to 1000 eV, electron, ion and coincidence spectroscopy studies can be executed in a very broad photon energy range.
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| 10. |
- Kooser, Kuno, et al.
(författare)
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Operando high-temperature near-ambient pressure X-ray photoelectron spectroscopy and impedance spectroscopy study of Ni−Ce0.9Gd0.1O2−δ solid oxide fuel cell anode
- 2020
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 45:46, s. 25286-25298
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Tidskriftsartikel (refereegranskat)abstract
- In this study we present the results of operando high temperature near-ambient-pressure x-ray photoelectron spectroscopy (HT-NAP-XPS) measurements of a pulsed laser deposited thin film Ni−Ce0.9Gd0.1O2−δ model electrode. In our measurements, we have used the novel three electrode dual-chamber electrochemical cell developed in our previous work at different H2 pressures and at different electrochemical conditions at around 650 °C. The possible redox reactions on the anode surface (Ni2+↔Ni0,Ce4+↔Ce3+) were investigated by HT-NAP-XPS technique simultaneously with electrochemical impedance spectroscopy measurements. The oxygen partial pressure in counter and reference electrode compartment was controlled at 0.2 bar. Changes in electronic structure of the Ce3d and Ni2p photoelectron spectra caused by electrode potential and H2 pressure variations were observed and estimated by curve fitting procedure. The O1s and valence band photoelectron signals were used for depth probing of the chemical composition and redox changes at Ni-GDC and for studying the influence of the electrochemical polarization on the chemical state of Ni-GDC surface atoms. As a result changes in oxidation state of electrode surface atoms caused by electrode polarization and oxide ion flux through the membrane were detected with simultaneous significant variation of electrochemical impedance.
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