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Träfflista för sökning "WFRF:(Kukk E) srt2:(2010-2014)"

Sökning: WFRF:(Kukk E) > (2010-2014)

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1.
  • Itala, E, et al. (författare)
  • Molecular fragmentation of pyrimidine derivatives following site-selective carbon core ionization
  • 2011
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 184:3-6, s. 119-124
  • Tidskriftsartikel (refereegranskat)abstract
    • Ionization-site-dependent fragmentation of three cyclic biomolecules - uracil, 5-bromouracil and thymine - has been studied using electron-energy-resolved photoelectronphotoion-photoion coincidence spectroscopy. Previous studies concerning ionization site dependent fragmentation have mainly been carried out with linear molecules. The results reported here show that all studied molecules have dicationic fragmentation channels whose intensity depends on the initial core-ionization site, although these channels cover only a relatively small fraction of the total fragment yield. The present study shows on one hand, that it is often the surrounding bond(s) of the ionized atom that will break following the initial core ionization, and on the other hand, that some specific fragmentation channels can display strong site-dependency where there is no direct correlation between the ionization site and the bond breakage locations.
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2.
  • Kokko, K., et al. (författare)
  • Atomistic study of surfaces and interfaces of Fe-Cr and Fe-Cr-Al alloys
  • 2013
  • Ingår i: Physical and numerical simulation of materials processing VII. - : Trans Tech Publications Inc.. - 9783037857281 ; , s. 728-733
  • Konferensbidrag (refereegranskat)abstract
    • Surface and interface properties of Fe-Cr, Fe-Al, and Fe-Cr-Al are studied using Exact Muffin-Tin Orbitals and Monte Carlo methods and with x-ray photoelectron and Auger electron techniques. Surface composition is investigated as a function of oxidation (heating) time. Hard x ray photoelectron spectroscopy (HAXPES) is used to scan non destructively the compositions below the surface. It is found that Cr boosts the Al segregation to the surface.
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3.
  • Fukuzawa, H., et al. (författare)
  • Deep Inner-Shell Multiphoton Ionization by Intense X-Ray Free-Electron Laser Pulses
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 110:17
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated multiphoton multiple ionization dynamics of xenon atoms using a new x-ray free-electron laser facility, SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan, and identified that Xen+ with n up to 26 is produced at a photon energy of 5.5 keV. The observed high charge states (n >= 24) are produced via five-photon absorption, evidencing the occurrence of multiphoton absorption involving deep inner shells. A newly developed theoretical model, which shows good agreement with the experiment, elucidates the complex pathways of sequential electronic decay cascades accessible in heavy atoms. The present study of heavy-atom ionization dynamics in high-intensity hard-x-ray pulses makes a step forward towards molecular structure determination with x-ray free-electron lasers. DOI: 10.1103/PhysRevLett.110.173005
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4.
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5.
  • Ha, Dang Trinh, et al. (författare)
  • Fragmentation Dynamics of Doubly Charged Methionine Phase
  • 2014
  • Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 118:8, s. 1374-1383
  • Tidskriftsartikel (refereegranskat)abstract
    • The dependence of the fragmentation of doubly charged gas-phase methionine (C5H11NO2S) on the electronic-state character of the parent ion is studied experimentally by energy-resolved electron ion-ion coincidence spectroscopy. The parent dication electronic states are populated by Auger transitions following site-specific sulfur 2p core ionization. Two fragmentation channels are observed to be strongly dependent on the electronic states with vacancies in weakly bound molecular orbitals. All-electron calculations are applied to assign doubly charged final states of sulfur 2p core ionized methionine. In addition, the Car-Parrinello method is applied to model fragmentation dynamics of doubly charged methionine molecules with various initial temperatures to understand the typical characteristics of the molecular dissociation and partly to support the interpretation of experimental data.
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6.
  • Itala, E., et al. (författare)
  • A comparative study of dissociation of thymidine molecules following valence or core photoionization
  • 2013
  • Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:21, s. 215102-
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied the fragmentation of gas phase thymidine following valence and core ionization using synchrotron radiation, combined with electron energy and ion mass resolved detection in coincidence. To identify certain fragment masses C-13 labelled thymidine was also used. We find that in large part, the photofragmentation of thymidine can be described as separated thymine and 2-deoxy-D-ribose cations. However, also the intact thymidine radical cation, formation of intact base and sugar cations from glycosidic bond cleavage and several new thymidine-specific fragments are observed after valence ionization. Conversely, at the photoionization of C 1s electrons neither parent thymidine cations nor any fragments above 55 amu were detected, and only ion pairs with small masses survive core ionization, Auger decay and the subsequent Coulomb separation of the DNA sub-unit. This demonstrates the genotoxic nature of soft x-rays which in cells induce complex clustered damage similar to those yielded by heavy particles.
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7.
  • Itala, E., et al. (författare)
  • Fragmentation patterns of core-ionized thymine and 5-bromouracil
  • 2010
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:15, s. 154316-
  • Tidskriftsartikel (refereegranskat)abstract
    • Photofragmentation of thymine and 5-bromouracil into cation and neutral fragments following the core ionization by soft x-rays using photoelectron-photoion-photoion coincidence technique has been studied. The fragment ion mass spectra were recorded in coincidence with the C 1s photoelectron spectra. In the case of thymine, deuterated samples were used to identify fragments. Deuteration or bromination allowed us to study not only the main fragmentation channels of these pyrimidine bases, but also to investigate if replacement of an exocyclic functional group affects molecular fragmentation. We found that the dominant fragmentation channels involve only one starting geometry, and the base ring and other bond cleavages, leading to the detected fragments, are essentially identical between thymine and 5-bromouracil. In addition, the relative intensities of the strongest fragmentation channels were determined and compared with calculated appearance energies using ab initio unrestricted Hartree-Fock theory. (C) 2010 American Institute of Physics. [doi:10.1063/1.3505140]
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8.
  • Itälä, E., et al. (författare)
  • Photofragmentation of a DNA nucleoside thymidine; Valence-vs. core ionization
  • 2012
  • Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:PART 2, s. 022078-
  • Tidskriftsartikel (refereegranskat)abstract
    • The photofragmentation of free thymidine molecule has been studied using combined electron- and ion spectroscopy. The results show that valence- and core ionization processes produce very different fragmentation patterns and that regardless of the photon energy, the photoionization leads almost always to dissociation of the thymidine molecule.
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9.
  • Itälä, E., et al. (författare)
  • Soft x-ray ionization induced fragmentation of glycine
  • 2014
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:23, s. 234305-
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray absorption commonly involves dissociative core ionization producing not only momentum correlated charged fragments but also low-and high-energy electrons capable of inducing damage in living tissue. This gives a natural motivation for studying the core ionization induced fragmentation processes in biologically important molecules such as amino acids. Here the fragmentation of amino acid glycine following carbon 1s core ionization has been studied. Using photoelectron-photoion-photoion coincidence technique, a detailed analysis on fragmentation of the sample molecule into pairs of momentum correlated cations has been carried out. The main characteristics of core ionization induced fragmentation of glycine were found to be the rupture of the C-C a bond and the presence of the CNH2+ fragment.
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10.
  • Kooser, K., et al. (författare)
  • Size selective spectroscopy of Se microclusters
  • 2012
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure and photofragmentation in outer and inner valence regions of Se-n (n <= 8) clusters produced by direct vacuum evaporation have been studied with size-selective photoelectron-photoion coincidence technique by using vacuum-ultraviolet synchrotron radiation. The experimental ionization potentials of these clusters were extracted from the partial ion yield measurements. The calculations for the possible geometrical structures of the Se-n microclusters have been executed. The ionization energies of the clusters have been calculated and compared with the experimental results. In addition, theoretical fragment ion appearance energies were estimated. The dissociation energies of Se-n clusters were derived from the recurrent relation between the gas phase enthalpies of the formation of corresponding cationic clusters and experimental ionization energies. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737633]
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