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Sökning: WFRF:(Kukk E)

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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.
  • Kukk, E., et al. (författare)
  • Formative period in the x-ray-induced photodissociation of organic molecules
  • 2021
  • Ingår i: Physical Review Research. - 2643-1564. ; 3:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Absorption of x-ray photons by atomic inner shells of light-element organics and biomolecules often leads to formation of dicationic electronic states and to molecular fragmentation. We investigated the x-ray-induced dissociation landscape of a representative medium-sized organic molecule, thiophene, by femtosecond x-ray pulses from the Super Photon Ring-8 GeV (SPring-8) Angstrom Compact Free-Electron Laser (SACLA). Holes, created in the sulfur 2p orbital by photoemission, were filled by the Auger process that created dicationic molecular states within a broad range of internal energies—a starting point particular to x-ray-induced dynamics. The evolution of the ionized molecules was monitored by a pump-probe experiment using a near-infrared (800 nm) laser pulse. Ion-ion coincidence and ion momentum analysis reveals enhanced yields of ionic fragments from multibody breakup of the ring, attributed to additional ionization of the highly excited fraction of the dicationic parent molecular states. The transient nature of the enhancement and its decay with about a 160-fs time constant indicate formation of an open-ring parent geometry and the statistical survival time of the parent species before the dissociation events. By probing specific Auger final states of transient, highly excited nature by near-infrared light, we demonstrate how pump-probe signatures can be related to the key features in dynamics during the early period of the x-ray-induced damage of organic molecules and biomolecules.
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4.
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5.
  • Thomas, T.D., et al. (författare)
  • Photoelectron-recoil-induced rotational excitation of the B 2 state in N2
  • 2009
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 79:022506
  • Tidskriftsartikel (refereegranskat)abstract
    • In the photoelectron spectrum of N-2 the apparent ionization energy to form the B (2)Sigma(+)(u) state increases linearly with the photon energy. Rotationally resolved measurements of the fluorescent decay of this state show a linear increase of rotational heating with increasing photon energy. These results are in quantitative agreement with the prediction of the theory of recoil-induced rotational excitation, indicating that the rotational heating that has been observed previously arises primarily from such recoil-induced excitation. Together with other results that have been reported they show that recoil-induced internal excitation is significant in many situations, including near threshold.
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6.
  • AKSELA, H, et al. (författare)
  • PARTIAL AUGER DECAY-RATES OF CORE-IONIZED MOLECULAR-STATES IN HCL AND DCL
  • 1995
  • Ingår i: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP PUBLISHING LTD. - 0953-4075. ; 28:19, s. 4259-4268
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The Cl 2p ionization and the subsequent 2p(-1) --> 2 pi(-2) Auger decay in HCl and DCl molecules have been studied using synchrotron radiation. The Anger spectra have been decomposed and assigned to the transitions from the (2) Pi(1/2), (2) Sigma(1/2) and
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7.
  • 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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8.
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9.
  • 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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10.
  • 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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11.
  • 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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12.
  • 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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13.
  • 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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14.
  • Jahnke, T., et al. (författare)
  • Inner-Shell-Ionization-Induced Femtosecond Structural Dynamics of Water Molecules Imaged at an X-Ray Free-Electron Laser
  • 2021
  • Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 11:4
  • 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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15.
  • 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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16.
  • Kukk, E, et al. (författare)
  • Auger decay of the dissociating core-excited states in the HCl and DCl molecules
  • 1996
  • Ingår i: JOURNAL OF CHEMICAL PHYSICS. - : AMER INST PHYSICS. ; 104:12, s. 4475-4480
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • High-resolution Auger electron spectra from the decay of the Cl 2p-->sigma* excitation in HCl and DCl have been measured. The spectra are analyzed, separating molecular and atomic features, which are assigned to transitions to the HCl (5 sigma 2 pi)(4) si
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17.
  • Kukk, E, et al. (författare)
  • Core-to-Rydberg excitations and their Auger decay in the HCl and DCl molecules
  • 1996
  • Ingår i: PHYSICAL REVIEW A. - : AMER INST PHYSICS. - 1050-2947. ; 54:3, s. 2121-2126
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The resonant Anger electron spectra of the HCl and DCl molecules have been measured at the first core-to-Rydberg resonances. The low binding energy region of the spectra has been decomposed into transitions to different bound states and their vibrational
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18.
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19.
  • Kukk, E., et al. (författare)
  • Internal energy dependence in x-ray-induced molecular fragmentation : An experimental and theoretical study of thiophene
  • 2015
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 91:4
  • Tidskriftsartikel (refereegranskat)abstract
    • A detailed experimental and theoretical investigation of the dynamics leading to fragmentation of doubly ionized molecular thiophene is presented. Dissociation of double-ionized molecules was induced by S 2p core photoionization and the ionic fragments were detected in coincidence with Auger electrons from the core-hole decay. Rich molecular dynamics was observed in electron-ion-ion coincidence maps exhibiting ring breaks accompanied by hydrogen losses and/or migration. The probabilities of various dissociation channels were seen to be very sensitive to the internal energy of the molecule. Theoretical simulations were performed by using the semiempirical self-consistent charge-density-functional tight-binding method. By running thousands of these simulations, the initial conditions encountered in the experiment were properly taken into account, including the systematic dependencies on the internal (thermal) energy. This systematic approach, not affordable with first-principle methods, provides a good overall description of the complex molecular dynamics observed in the experiment and shows good promise for applicability to larger molecules or clusters, thus opening the door to systematic investigations of complex dynamical processes occurring in radiation damage.
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20.
  • Kukk, E., et al. (författare)
  • Molecular dynamics of photodissociation : towards more complex systems
  • 2015
  • Ingår i: XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12. - : Institute of Physics Publishing (IOPP).
  • Konferensbidrag (refereegranskat)abstract
    • We present a combined experimental and theoretical study of the photodissociation of thiophene molecule using energy-resolved electron-ion-ion coincidence technique and self-consistent charge density functional tight-binding theory combined with a statistical approach. The observed complex molecular dynamics with many internal-energy-dependent fragmentation pathways is successfully described by the theoretical simulations.
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21.
  • Laksman, J., et al. (författare)
  • Dissociation Pathways in the Cysteine Dication after Site-Selective Core Ionization
  • 2014
  • Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:40, s. 11688-11695
  • Tidskriftsartikel (refereegranskat)abstract
    • A photoelectronionion coincidence experiment has been carried out on the amino acid molecule cysteine after core-ionization of the O 1s, N 1s, C 1s, and S 2p orbitals. A number of different dissociation channels have been identified. Some of them show strong site-selective dependence that can be attributed to a combination of nuclear motion in the core-ionized state and Auger processes that populate different final electronic states in the dication.
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22.
  • Levola, H., et al. (författare)
  • Fragmentation of thymidine induced by ultraviolet photoionization and thermal degradation
  • 2013
  • Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806 .- 1873-2798. ; 353, s. 7-11
  • Tidskriftsartikel (refereegranskat)abstract
    • Fragmentation of gas phase thymidine at different temperatures was studied with vacuum ultraviolet radiation and time-of-flight spectroscopy. Partial ion yield measurements were carried out in order to study the appearance energies of thymidine and its main fragments. The appearance energies of thymidine and its deoxyribose- and thymine-based fragments were determined to be 8.39, 8.77 and 8.81 eV, independently of temperature. The thermal decomposition of the sample was observed to start around 138-139 C and it was explained by the breakage of the glycosidic bond, accompanied by hydrogen transfer from the deoxyribose ring to the thymine base.
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23.
  • Motomura, K., et al. (författare)
  • Sequential multiphoton multiple ionization of atomic argon and xenon irradiated by X-ray free-electron laser pulses from SACLA
  • 2013
  • Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated multiphoton multiple ionization of argon and xenon atoms at 5 keV using a new x-ray free electron laser (XFEL) facility, the SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan. The experimental results are compared with the new theoretical results presented here. The absolute fluence of the XFEL pulse has been determined with the help of the calculations utilizing two-photon processes in the argon atom. The high charge states up to +22 observed for Xe in comparison with the calculations point to the occurrence of sequential L-shell multiphoton absorption and of resonance-enabled x-ray multiple ionization.
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24.
  • Murphy, B. F., et al. (författare)
  • Femtosecond X-ray-induced explosion of C-60 at extreme intensity
  • 2014
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding molecular femtosecond dynamics under intense X-ray exposure is critical to progress in biomolecular imaging and matter under extreme conditions. Imaging viruses and proteins at an atomic spatial scale and on the time scale of atomic motion requires rigorous, quantitative understanding of dynamical effects of intense X-ray exposure. Here we present an experimental and theoretical study of C-60 molecules interacting with intense X-ray pulses from a free-electron laser, revealing the influence of processes not previously reported. Our work illustrates the successful use of classical mechanics to describe all moving particles in C-60, an approach that scales well to larger systems, for example, biomolecules. Comparisons of the model with experimental data on C-60 ion fragmentation show excellent agreement under a variety of laser conditions. The results indicate that this modelling is applicable for X-ray interactions with any extended system, even at higher X-ray dose rates expected with future light sources.
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25.
  • Patanen, M., et al. (författare)
  • High-resolution study of K 3p photoabsorption and resonant Auger decay in KF
  • 2009
  • Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 80:1
  • Tidskriftsartikel (refereegranskat)abstract
    • High-resolution (K3p sigma and pi)->sigma absorption spectrum of KF in the photon energy range of 18.2-19.4 eV was measured at the new FINEST beamline branch on the I3 beamline on MAX III. The experimental spectrum is presented and interpreted using nonrelativistic ab initio molecular calculations corrected with perturbation theory treatment to account for spin-orbit interaction. Resonant Auger decay recorded at the strongest resonances is also presented and reproduced by theoretical calculations. Also a brief introduction to the FINEST beamline branch is presented.
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26.
  • Pärna, R., et al. (författare)
  • FinEstBeaMS – A wide-range Finnish-Estonian Beamline for Materials Science at the 1.5 GeV storage ring at the MAX IV Laboratory
  • 2017
  • Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 859, s. 83-89
  • Tidskriftsartikel (refereegranskat)abstract
    • The FinEstBeaMS beamline is under construction at the 1.5 GeV storage ring of the MAX IV Laboratory at Lund, Sweden. It has been designed to cover an unusually wide energy range from ultraviolet (4.3 eV) to soft X-rays (1000 eV) but experiments will also be possible at the Mg and Al Kα energies. Instead of having two different insertion devices and optical schemes for low and high photon energy regions, we have based our design on a single long-period, elliptically polarizing undulator and a plane grating monochromator. This solution will provide very good conditions for planned experiments in the whole photon energy region. The beamline will have two branches: one will mainly be used to investigate free atoms, molecules and clusters with photoelectron/photoion coincidence spectroscopy as well as solids with photoluminescence spectroscopy whereas the other one will be dedicated to ultra-high vacuum studies of surfaces and interfaces, utilizing X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. This paper focuses on the optical design of the beamline and general design concepts of the gas phase and solid state end stations.
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27.
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28.
  • Travnikova, O., et al. (författare)
  • Ultrafast dissociation of ammonia : Auger Doppler effect and redistribution of the internal energy
  • 2022
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:10, s. 5842-5854
  • Tidskriftsartikel (refereegranskat)abstract
    • We study vibrationally-resolved resonant Auger (RAS) spectra of ammonia recorded in coincidence with the NH2+ fragment, which is produced in the course of dissociation either in the core-excited 1s−14a11 intermediate state or the first spectator 3a−24a11 final state. Correlation of the NH2+ ion flight times with electron kinetic energies allows directly observing the Auger-Doppler dispersion for each vibrational state of the fragment. The median distribution of the kinetic energy release EKER, derived from the coincidence data, shows three distinct branches as a function of Auger electron kinetic energy Ee: Ee + 1.75EKER = const for the molecular band; EKER = const for the fragment band; and Ee + EKER = const for the region preceding the fragment band. The deviation of the molecular band dispersion from Ee + EKER = const is attributed to the redistribution of the available energy to the dissociation energy and excitation of the internal degrees of freedom in the molecular fragment. We found that for each vibrational line the dispersive behavior of EKERvs. Ee is very sensitive to the instrumental uncertainty in the determination of EKER causing the competition between the Raman (EKER + Ee = const) and Auger (Ee = const) dispersions: increase in the broadening of the finite kinetic energy release resolution leads to a change of the dispersion from the Raman to the Auger one. 
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29.
  • Urpelainen, S., et al. (författare)
  • FINEST:A high performance branch-line for VUV photon energy range gas phase studies at MAX-lab
  • 2010
  • Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. - 9780735407824 ; 1234, s. 411-414
  • Konferensbidrag (refereegranskat)abstract
    • We present a dedicated beamline branch for high flux and ultra-high resolution (R>100000) gas and vapor phase studies in the vacuum-ultra-violet (VUV) region of light on the undulator beamline I3, located on the 700 MeV MAX-III storage ring. The mechanical and optical design of the branch-line, the differential pumping setup as well as performance characteristics are presented.
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30.
  • Achen, M G, et al. (författare)
  • Vascular endothelial growth factor D (VEGF-D) is a ligand for the tyrosine kinases VEGF receptor 2 (Flk1) and VEGF receptor 3 (Flt4).
  • 1998
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 95:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We have identified a member of the VEGF family by computer-based homology searching and have designated it VEGF-D. VEGF-D is most closely related to VEGF-C by virtue of the presence of N- and C-terminal extensions that are not found in other VEGF family members. In adult human tissues, VEGF-D mRNA is most abundant in heart, lung, skeletal muscle, colon, and small intestine. Analyses of VEGF-D receptor specificity revealed that VEGF-D is a ligand for both VEGF receptors (VEGFRs) VEGFR-2 (Flk1) and VEGFR-3 (Flt4) and can activate these receptors. However. VEGF-D does not bind to VEGFR-1. Expression of a truncated derivative of VEGF-D demonstrated that the receptor-binding capacities reside in the portion of the molecule that is most closely related in primary structure to other VEGF family members and that corresponds to the mature form of VEGF-C. In addition, VEGF-D is a mitogen for endothelial cells. The structural and functional similarities between VEGF-D and VEGF-C define a subfamily of the VEGFs.
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31.
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32.
  • Carniato, S., et al. (författare)
  • Hybrid density-functional theory calculations of near-edge x-ray absorption fine-structure spectra : Applications on benzonitrile in gas phase
  • 2005
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 71:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The experimental N(1s) near-edge x-ray-absorption fine-structure spectrum of the benzonitrile molecule in the gas phase shows well separated double peaks with different vibrational profiles. Hybrid density-functional theory calculations reveal that such a separation is a result of the conjugation effect on the nitrogen 2p orbitals and the double spectral peaks can be assigned as the N(1s)-pi* out-of-plane and in-plane resonances. The vibrational profiles have been analyzed using a combined transition state theory and linear coupling model. Each profile consists of two different vibrational progressions corresponding to stretching modes and a broad continuum of bending excited states. The use of transition state theory allows identifying the dynamics of the N 1s core excitation. It is found that upon core excitations the C-N bond of the benzonitrile molecule can go from initial linear to final bent structures through different paths. The calculated spectrum is in excellent agreement with experiment.
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33.
  • Carniato, S., et al. (författare)
  • Multidimensional transition-state theory calculations for nuclear dynamics of core-excited molecules
  • 2004
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 70:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We have extended the transition-state theory to describe the dynamics of core hole excitation. This allows us to interpret the abnormally bland near-edge x-ray absorption fine structure spectrum of the gas phase benzonitrile molecule at the N 1s edge. We have brought to light different paths for the two most intensive resonances, going from the linear to the bent structure. The profile of each resonance consists of two different vibrational progressions corresponding to stretching modes and a broad continuum of bending excited states.
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34.
  • Fang, L., et al. (författare)
  • Multiple Ionization and Double Core-hole Production in Molecules using the LCLS X-ray FEL
  • 2012
  • Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:3, s. 032028-
  • 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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35.
  • Guillemin, R., et al. (författare)
  • Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser
  • 2023
  • Ingår i: STRUCTURAL DYNAMICS-US. - 2329-7778. ; 10:5
  • 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.
  •  
36.
  • Kukk, E., et al. (författare)
  • Dissociation of deuteromethane following carbon 1s core ionization
  • 2002
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 66:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Energy-resolved electron-ion coincidence spectra of the deuteromethane molecule were measured following ionization by narrow-band synchrotron radiation. The ion mass spectra were recorded in coincidence with the outer and inner valence photoelectrons and with the normal Auger electrons from the decay of the carbon 1s core hole. Complementary noncoincidence ion mass spectra were measured below and above the C 1s threshold. The fragmentation patterns of the singly and doubly ionized deuteromethane under different ionization conditions are examined. Carbon core ionization is shown to open new photodissociation pathways not available in the valence ionization photon energy regime. With the aid of ab initio quantum chemistry calculations, a two-step model of the dissociation following core ionization is proposed, showing a good agreement with the experimental findings.
  •  
37.
  • Kukk, E., et al. (författare)
  • Electronic state dependence in the dissociation of core-ionized methane
  • 2007
  • Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:18, s. 3677-3692
  • Tidskriftsartikel (refereegranskat)abstract
    • Methane and deuteromethane molecules were core ionized using synchrotron radiation, and the ionic fragments from the molecular dissociation were detected in coincidence with the Auger electrons. The electron - ion coincidence spectra are analysed in terms of partial ion yields and ion kinetic energy distributions, both as functions of electron kinetic energy. The dependence of the fragmentation patterns on the electronic character of the Auger final states as well as on the excess energy available for dissociating the molecule is studied. The analysis reveals marked differences in the dissociation of the 2a(1)(-2) and 2a(1)(-1) 1t(2)(-1) states, interpreted as an `excess- energy- dependent' concerted dissociation process for the 2a(1)(-2) state and an ` electronic- state- dependent' sequential process for the 2a(1)(-1) 1t(2)(-1) state.
  •  
38.
  • Kukk, E., et al. (författare)
  • Energy-dependent timescales in the dissociation of diiodothiophene dication
  • 2023
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 25:7, s. 5795-5807
  • Tidskriftsartikel (refereegranskat)abstract
    • Photodissociation molecular dynamics of gas-phase 2,5-diiodothiophene molecules was studied in an electron-energy-resolved electron-multi-ion coincidence experiment performed at the FinEstBeAMS beamline of MAX IV synchrotron. Following the photoionization of the iodine 4d subshell and the Auger decay, the dissociation landscape of the molecular dication was investigated as a function of the Auger electron energy. Concentrating on an major dissociation pathway, C4H2I2S2+ -> C4H2S+ + I+ + I, and accessing the timescales of the process via ion momentum correlation analysis, it was revealed how this three-body process changes depending on the available internal energy. Using a generalized secondary dissociation model, the process was shown to evolve from secondary dissociation regime towards concerted dissociation as the available energy increased, with the secondary dissociation time constant changing from 1.5 ps to 129 fs. The experimental results were compared with simulations using a stochastic charge-hopping molecular mechanics model. It represented the observed trend and also gave a fair quantitative agreement with the experiment.
  •  
39.
  • Kukk, E., et al. (författare)
  • Energy Transfer into Molecular Vibrations and Rotations by Recoil in Inner-Shell Photoemission
  • 2018
  • Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 121:7
  • Tidskriftsartikel (refereegranskat)abstract
    • A mixture of CF4 and CO gases is used to study photoelectron recoil effects extending into the tender xray region. In CF4, the vibrational envelope of the C 1s photoelectron spectrum becomes fully dominated by the recoil-induced excitations, revealing vibrational modes hidden from Franck-Condon excitations. In CO, using CF4 as an accurate energy calibrant, we determine the partitioning of the recoil-induced internal excitation energy between rotational and vibrational excitation. The observed rotational recoil energy is 2.88(28) times larger than the observed vibrational recoil energy, well in excess of the ratio of 2 predicted by the basic recoil model. The experiment is, however, in good agreement with the value of 2.68 if energy transfer via Coriolis coupling is included.
  •  
40.
  • Kukk, E., et al. (författare)
  • Photoelectron recoil in CO in the x-ray region up to 7 keV
  • 2017
  • Ingår i: PHYSICAL REVIEW A. - 2469-9926. ; 95:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon 1s photoelectron spectra of CO molecules in gas phase were recorded in the tender x-ray energy range, from 2.3 to 6.9 keV. The intensity ratios of individual peaks from nu = 0 to 3 within the vibrational progression of the C 1s photoelectron spectrum were determined at the various photon energies and are shown to be strongly affected by the photoelectron recoil effect. The experimental vibrational intensity ratios are compared with theoretical predictions at different levels of accuracy. Developments of the recoil model, using generalized Franck-Condon factors, rovibrational coupling, Morse potential energy curves, and accurate angular averaging are presented and applied to the analysis of the experimental results.
  •  
41.
  • Kukk, E, et al. (författare)
  • Raman versus non-Raman behavior in resonant auger spectra of HCl
  • 1996
  • Ingår i: PHYSICAL REVIEW LETTERS. - : AMER INST PHYSICS. ; 76:17, s. 3100-3103
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Two different types of Anger processes are shown to constitute the resonant Anger spectra of HCl: one which does and one which does not show Raman narrowing with the decrease of the spectral width of the exciting radiation. An analytical explanation for t
  •  
42.
  • Kukk, E., et al. (författare)
  • Unified treatment of recoil and Doppler broadening in molecular high-energy photoemission
  • 2021
  • Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 23:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Doppler and recoil effects are an integral part of the photoemission process at the high kinetic energies reached in hard x-ray photo-electron spectroscopy (HAXPES) and have a major effect on the observed lineshape, resulting in broadening, energy losses and discrete excitations. These effects can be modeled with a high degree of detail for small systems like diatomic molecules, for larger systems such treatment is often superfluous as the fine spectral features are not observable. We present a united description of the Doppler and recoil effects for arbitrary polyatomic systems and offer an approximate description of the recoil- and Doppler-modified photoemission spectral lineshape as a practical tool in the analysis of HAXPES spectra of core-level photoemission. The approach is tested on the examples of carbon dioxide and pentane molecules. The C and O 1s photoelectron spectra of CO2 in gas phase were also measured at 2.3 and 7.0 keV photon energy at Synchrotron SOLEIL and the spectra were analyzed using the model description. The limitations and applicability of the approach to adsorbates, interfaces and solids is briefly discussed.
  •  
43.
  • Larsson, Mats, et al. (författare)
  • Double core-hole formation in small molecules at the LCLS free electron laser
  • 2013
  • Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16, s. 164030-
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated nonlinear processes in small molecules by x-ray photoelectron spectroscopy using the Linac Coherent Light Source free electron laser, and by simulations. The main focus of the experiments was the formation of the two-site double core-hole (tsDCH) states in the molecules CO2, N2O and N-2. These experiments are described in detail and the results are compared with simulations of the photoelectron spectra. The double core-hole states, and in particular the tsDCH states, have been predicted to be highly sensitive to the chemical environment. The theory behind this chemical sensitivity is validated by the experiments. Furthermore, our simulations of the relative integrated intensities of the peaks associated with the nonlinear processes show that this type of simulation, in combination with experimental data, provides a useful tool for estimating the duration of ultra-short x-ray pulses.
  •  
44.
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45.
  • Pihlava, L., et al. (författare)
  • Photodissociation dynamics of halogenated aromatic molecules: the case of core-ionized tetrabromothiophene
  • 2021
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:37, s. 21249-21261
  • Tidskriftsartikel (refereegranskat)abstract
    • We studied the gas-phase photodissociation of a fully halogenated aromatic molecule, tetrabromothiophene, upon core-shell ionization by using synchrotron radiation and energy-resolved multiparticle coincidence spectroscopy. Photodynamics was initiated by the selective soft X-ray ionization of three elements - C, S, and Br - leading to the formation of dicationic states by Auger decay. From a detailed study of photodissociation upon Br 3d ionization, we formulate a general fragmentation scheme, where dissociation into neutral fragments and a pair of cations prevails, but dicationic species are also produced. We conclude that dicationic tetrabromothiophene typically undergoes deferred charge separation (with one of the ions being often Br+) that may be followed by secondary dissociation steps, depending on the available internal energy of the parent dication. Observations suggest that the ejection of neutral bromine atoms as the first step of deferred charge separation is a prevailing feature in dicationic dissociation, although sometimes in this step the C-Br bonds appear to remain intact and the thiophene ring is broken instead. Ionization-site-specific effects are observed particularly in doubly charged fragments and as large differences in the yields of the intact parent dication. We interpret these effects, using first-principles calculations and molecular dynamics simulations of core-hole states, as likely caused by the geometry changes during the core-hole lifetime.
  •  
46.
  • Rius, J., et al. (författare)
  • Selective fragmentation of valence- and core-electron-excited CD4 and SF6 molecules
  • 2002
  • Ingår i: Surface review and letters. - 0218-625X. ; 9:1, s. 117-123
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron-ion coincidence measurements with energy-resolved electrons are a powerful tool in studies of molecular fragmentation processes, since fragmentation from a specific doorway state can be monitored while the remaining reactions are discriminated. Presently, we have applied this technique in measurements of coincidence spectra of the CD4 and SF6 molecules after valence and core electron excitation. The newly constructed energy-resolved electron-ion coincidence station developed for this project has been used. Our results on CD4 are the first demonstration of a correlation between vibrations and molecular dissociation observed in this molecule. The SF6 spectra reveal strong selectivity in dissociation following distinct electronic states of the molecule. This selectivity reflects the bonding properties of the potential surfaces involved in the studied processes. The obtained results exemplify the potential of the new multicoincidence station used in this work.
  •  
47.
  • Sahlén, Martin, et al. (författare)
  • Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-Ray Free-Electron Laser
  • 2012
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:15, s. 153003-
  • Tidskriftsartikel (refereegranskat)abstract
    • We have performed x-ray two-photon photoelectron spectroscopy using the Linac Coherent Light Source x-ray free-electron laser in order to study double core-hole (DCH) states of CO2, N2O, and N-2. The experiment verifies the theory behind the chemical sensitivity of two-site DCH states by comparing a set of small molecules with respect to the energy shift of the two-site DCH state and by extracting the relevant parameters from this shift.
  •  
48.
  • Saleacuten, P., et al. (författare)
  • X-ray FEL-induced Double Core-Hole Formation in Polyatomic Molecules
  • 2012
  • Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:2, s. 022083-
  • 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.
  •  
49.
  • Sankari, R, et al. (författare)
  • High resolution O 1s photoelectron shake-up satellite spectrum of H2O
  • 2006
  • Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 422:1-3, s. 51-57
  • Tidskriftsartikel (refereegranskat)abstract
    • The O 1s photoelectron satellite spectrum of water has been recorded with high resolution and some vibrational structures were detected. The electronic and vibrational structures observed in the experimental spectrum are well interpreted with the aid of the molecular ab initio calculations based on the symmetry adapted cluster-configuration interaction (SAC-CI) method. (c) 2006 Elsevier B.V. All rights reserved.
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50.
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