| 1. |
- Eland, John H. D., 1941, et al.
(författare)
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Wide range double photoionization spectra of N2 and CO2
- 2016
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 646, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- Using a magnetic bottle time-of-flight electron spectrometer we have measured double photoionisation spectra of N2 and CO2 covering the range from threshold up to the triple ionisation energies. The experiments demonstrate the use of a new asynchronous chopper in eight-bunch mode of the synchrotron radiation source SOLEIL. For CO22+ some broad bands in the Auger spectra are found to have multiple resolved counterparts in the photoionisation spectrum. All the bands in the Auger spectra have counterparts in the photoionisation spectra, where extra bands attributed to triplet states are present. In the spectrum of N22+ we suggest reassignment of one band.
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| 2. |
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| 3. |
- Fink, Reinhold, et al.
(författare)
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Specific production of very long-lived core-excited sulfur atoms by 2p(-1)sigma* excitation of the OCS molecule followed by ultrafast dissociation
- 2006
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Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 39:12, s. L269-L275
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Tidskriftsartikel (refereegranskat)abstract
- A core-excited sulfur state with a lifetime almost one order of magnitude longer than in molecular 2p core-hole states is selectively produced by ultrafast dissociation of S 2p -> sigma* excited OCS. Clear evidence for this is provided by strong atomic peaks (20% of the total intensity) in x-ray fluorescence but very weak ones (2%) in the corresponding resonant Auger spectrum. Corroborating the assignment of the spectra, ab initio calculations explain the enhanced lifetime: the Auger decay of the produced D-3(3) (2p(5)3p(5)) sulfur state is strongly decreased as it contradicts a newly derived propensity rule of the L2,3MM Auger decay.
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| 4. |
- 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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| 5. |
- Georgescu, Mariana-Iuliana, et al.
(författare)
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Multimodal Multi-Head Convolutional Attention with Various Kernel Sizes for Medical Image Super-Resolution
- 2023
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Ingår i: 2023 IEEE/CVF WINTER CONFERENCE ON APPLICATIONS OF COMPUTER VISION (WACV). - : IEEE COMPUTER SOC. - 9781665493468 - 9781665493475 ; , s. 2194-2204
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Konferensbidrag (refereegranskat)abstract
- Super-resolving medical images can help physicians in providing more accurate diagnostics. In many situations, computed tomography (CT) or magnetic resonance imaging (MRI) techniques capture several scans (modes) during a single investigation, which can jointly be used (in a multimodal fashion) to further boost the quality of super-resolution results. To this end, we propose a novel multimodal multi-head convolutional attention module to super-resolve CT and MRI scans. Our attention module uses the convolution operation to perform joint spatial-channel attention on multiple concatenated input tensors, where the kernel (receptive field) size controls the reduction rate of the spatial attention, and the number of convolutional filters controls the reduction rate of the channel attention, respectively. We introduce multiple attention heads, each head having a distinct receptive field size corresponding to a particular reduction rate for the spatial attention. We integrate our multimodal multi-head convolutional attention (MMHCA) into two deep neural architectures for super-resolution and conduct experiments on three data sets. Our empirical results show the superiority of our attention module over the state-of-the-art attention mechanisms used in super-resolution. Moreover, we conduct an ablation study to assess the impact of the components involved in our attention module, e.g. the number of inputs or the number of heads. Our code is freely available at https://github.com/lilygeorgescu/MHCA.
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| 6. |
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| 7. |
- Kimberg, Victor, et al.
(författare)
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Molecular potentials and wave function mapping by high-resolution electron spectroscopy and ab initio calculations
- 2013
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 195, s. 301-306
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Tidskriftsartikel (refereegranskat)abstract
- The recent development of high brightness 3rd generation soft X-ray sources and high energy resolution electron spectrometers made it possible to accurately trace quantum phenomena associated to the vibrational dynamics in core-excited molecules. The present paper reviews the recent results on mapping of vibrational wave functions and molecular potentials based on electron spectroscopy. We discuss and compare the mapping phenomena in various systems, stressing the advantages of the resonant X-ray scattering for studying of the nuclear dynamics and spectroscopic constants of small molecules. The experimental results discussed in the paper are most often accompanied by state-of-the-art ab initio calculations allowing for a deeper understanding of the quantum effects. Besides its fundamental interest, the vibrational wave function mapping is shown to be useful for the analysis of core- and valence-excited molecular states based on the reflection principle.
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| 8. |
- Kumagai, Yoshiaki, et al.
(författare)
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Suppression of thermal nanoplasma emission in clusters strongly ionized by hard x-rays
- 2021
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Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 54:4
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Tidskriftsartikel (refereegranskat)abstract
- Using electron and ion spectroscopy, we studied the electron and nuclear dynamics in similar to 50 000-atom large krypton clusters, following excitation with an intense hard x-ray pulse. Beyond the single pulse experiment, we also present the results of a time-resolved, x-ray pump-near-infrared probe measurement that allows one to learn about the time evolution of the system. After core ionization of the atoms by x-ray photons, trapped Auger and secondary electrons form a nanoplasma in which the krypton ions are embedded, according to the already published scenario. While the ion data show expected features, the electron emission spectra miss the expected pump-probe delay-dependent enhancement except for a slight enhancement in the energy range below 2 eV. Theoretical simulations help to reveal that, due to the deep trapping potential of the ions during the long time expansion accompanied by electron-ion recombination, thermal emission from the transient nanoplasma becomes quenched.
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| 9. |
- Kushawaha, Rajesh Kumar, et al.
(författare)
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From double-slit interference to structural information in simple hydrocarbons
- 2013
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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. ; 110:38, s. 15201-15206
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Tidskriftsartikel (refereegranskat)abstract
- Interferences in coherent emission of photoelectrons from two equivalent atomic centers in a molecule are the microscopic analogies of the celebrated Young's double-slit experiment. By considering inner-valence shell ionization in the series of simple hydrocarbons C2H2, C2H4, and C2H6, we show that double-slit interference is widespread and has built-in quantitative information on geometry, orbital composition, and many-body effects. A theoretical and experimental study is presented over the photon energy range of 70-700 eV. A strong dependence of the oscillation period on the C-C distance is observed, which can be used to determine bond lengths between selected pairs of equivalent atoms with an accuracy of at least 0.01 angstrom. Furthermore, we show that the observed oscillations are directly informative of the nature and atomic composition of the inner-valence molecular orbitals and that observed ratios are quantitative measures of elusive many-body effects. The technique and analysis can be immediately extended to a large class of compounds.
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| 10. |
- Liu, Ji-Cai, et al.
(författare)
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Multimode Resonant Auger Scattering from the Ethene Molecule
- 2011
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 115:18, s. 5103-5112
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Tidskriftsartikel (refereegranskat)abstract
- Resonant Auger spectra of ethene molecule have been measured with vibrational resolution at several excitation energies in the region of the C1s(-1)1b(2g)(π*) resonance. The main features observed in the experiment have been assigned and are accurately interpreted on the basis of ab initio multimode calculations. Theory explains the extended vibrational distribution of the resonant Auger spectra and its evolution as a function of the excitation energy by multimode excitation during the scattering process. As a result, the resonant Auger spectra display two qualitatively different spectral features following the Raman and non-Raman dispersion laws, respectively. Calculations show that two observed thresholds of formation of non-Raman spectral bands are related to the "double-edge" structure of the X-ray absorption spectrum.
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| 11. |
- Liu, Ji-Cai, et al.
(författare)
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Resonant x-ray second-harmonic generation in atomic gases
- 2019
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 100:6
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Tidskriftsartikel (refereegranskat)abstract
- We explore the x-ray second-harmonic generation process induced by resonant two-photon absorption in systems with inversion symmetry. We show that this process becomes allowed in the x-ray region due to nondipole contributions. It is found that, although a plane-wave pump field generates only a longitudinal second-harmonic field, a Gaussian pump beam creates also a radially polarized transverse second-harmonic field which is stronger than the longitudinal one. Contrary to the longitudinal component, the transverse second-harmonic field with zero intensity on the axis of the pump beam can run in free space. Our theory is applied to Ar and Ne atomic vapors and predicts an energy conversion efficiency of x-ray second-harmonic generation of 3.2 x 10(-11) and 1.3 x 10(-12), respectively.
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| 12. |
- Liu, Xiao-Jing, et al.
(författare)
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Einstein-Bohr recoiling double-slit gedanken experiment performed at the molecular level
- 2015
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Ingår i: Nature Photonics. - 1749-4885 .- 1749-4893. ; 9:2, s. 120-125
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Tidskriftsartikel (refereegranskat)abstract
- Double-slit experiments illustrate the quintessential proof for wave-particle complementarity. If information is missing about which slit the particle has traversed, the particle, behaving as a wave, passes simultaneously through both slits. This wave-like behaviour and corresponding interference is absent if 'which-slit' information exists. The essence of Einstein-Bohr's debate about wave-particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. To measure the recoil of a slit, the slits should move independently. We showcase a materialization of this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case owing to Doppler labelling of the counter-propagating atomic slits, in full agreement with Bohr's complementarity.
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| 13. |
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| 14. |
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| 15. |
- Miao, Quan, et al.
(författare)
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Rotational Doppler Effect : A Probe for Molecular Orbitals Anisotropy
- 2015
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 6:9, s. 1568-1572
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Tidskriftsartikel (refereegranskat)abstract
- The vibrationally resolved X-ray photoelectron spectra of X-2 Sigma(+)(g)(3 sigma(-1)(g)) and B-2 Sigma(+)(u)(2 sigma(-1)(u)) states of N-2(+) were recorded for different photon energies and orientations of the polarization vector. Clear dependencies of the spectral line widths on the X-ray polarization as well as on the symmetry of the final electronic states are observed. Contrary to the translational Doppler, the rotational Doppler broadening is sensitive to the photoelectron emission anisotropy. On the basis of theoretical modeling, we suggest that the different rotational Doppler broadenings observed for gerade and ungerade final states result from a Young's double-slit interference phenomenon.
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| 16. |
- Miron, Catalin, et al.
(författare)
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Imaging molecular potentials using ultrahigh-resolution resonant photoemission
- 2012
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Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 8:2, s. 135-138
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Tidskriftsartikel (refereegranskat)abstract
- Electron-density distributions and potential-energy surfaces are important for predicting the physical properties and chemical reactivity of molecular systems. Whereas angle-resolved photoelectron spectroscopy enables the reconstruction of molecular-orbital densities of condensed species(1), absorption or traditional photoelectron spectroscopy are widely employed to study molecular potentials of isolated species. However, the information they provide is often limited because not all vibrational substates are excited near the vertical electronic transitions from the ground state. Moreover, many electronic states cannot be observed owing to selection rules or low transition probabilities. In many other cases, the extraction of the potentials is impossible owing to the high densities of overlapping electronic states. Here we use resonant photoemission spectroscopy, where the absence of strict dipole selection rules in Auger decay enables access to a larger number of final states as compared with radiative decay. Furthermore, by populating highly excited vibrational substates in the intermediate core-excited state, it is possible to 'pull out' molecular states that were hidden by overlapping spectral regions before.
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| 17. |
- Miron, Catalin, et al.
(författare)
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Multipathway dissociation dynamics of core-excited methyl chloride probed by high resolution electron spectroscopy and Auger-electron-ion coincidences
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:15, s. 154314-
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Tidskriftsartikel (refereegranskat)abstract
- Core excitation triggers nuclear dynamics on the femtosecond time scale. A multiparametric electron/ion coincidence approach has been used to disentangle complex decay processes occurring at short (molecular) or long (atomic) time scales. Methyl chloride has been excited by scanning along the dissociative Cl2p ->sigma* resonance. The detailed chronology of the competing decay processes, leading to either the rearrangement product HCl+, or an ultrafast dissociation leading to Cl+, has been investigated. The observed Auger- Doppler shift has been analyzed for various orientations of the electron and fragment ion.
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| 18. |
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| 19. |
- Miron, Catalin, et al.
(författare)
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Site-selective photoemission from delocalized valence shells induced by molecular rotation
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3816-
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Tidskriftsartikel (refereegranskat)abstract
- Due to the generally delocalized nature of molecular valence orbitals, valence-shell spectroscopies do not usually allow to specifically target a selected atom in a molecule. However, in X-ray electron spectroscopy, the photoelectron momentum is large and the recoil angular momentum transferred to the molecule is larger when the photoelectron is ejected from a light atom compared with a heavy one. This confers an extreme sensitivity of the rotational excitation to the ionization site. Here we show that, indeed, the use of high-energy photons to photoionize valence-shell electrons of hydrogen chloride offers an unexpected way to decrypt the atomic composition of the molecular orbitals due to the rotational dependence of the photoionization profiles. The analysis of the site-specific rotational envelopes allows us to disentangle the effects of the two main mechanisms of rotational excitation, based on angular momentum exchange between the molecule and either the incoming photon or the emitted electron.
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| 20. |
- Miron, Catalin, et al.
(författare)
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Vibrational Scattering Anisotropy Generated by Multichannel Quantum Interference
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:9, s. 093002-
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Tidskriftsartikel (refereegranskat)abstract
- Based on angularly and vibrationally resolved electron spectroscopy measurements in acetylene, we report the first observation of anomalously strong vibrational anisotropy of resonant Auger scattering through the C 1s --> pi* excited state. We provide a theoretical model explaining the new phenomenon by three coexisting interference effects: (i) interference between resonant and direct photoionization channels, (ii) interference of the scattering channels through the core-excited bending states with orthogonal orientation of the molecular orbitals, (iii) scattering through two wells of the double-well bending mode potential. The interplay of nuclear and electronic motions offers in this case a new type of nuclear wave packet interferometry sensitive to the anisotropy of nuclear dynamics: whether which-path information is available or not depends on the final vibrational state serving for path selection.
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| 21. |
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| 22. |
- Mocellin, Alexandra, et al.
(författare)
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Site selective dissociation upon core ionization of ozone
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 435:4-6, s. 214-218
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Tidskriftsartikel (refereegranskat)abstract
- Ozone is found to exhibit substantial site-selective fragmentation when its fragment ions are collected in coincidence with energy selected electrons. We find a preferential production of the O-2(+)/O+(O+/O+) ion pair upon ionization of the terminal (central) oxygen Is electron. Depending on the hole localization, Auger rates are different towards the various final states of the dication, which would produce the observed different fragmentation pattern. We also observe however an increase O-2(+)/O+ production for when the terminal core-hole state is vibrationally excited. This shows the role of the nuclear motion before the Auger decay in the observed site-specific.
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| 23. |
- Nandi, Saikat, et al.
(författare)
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Generation of entanglement using a short-wavelength seeded free-electron laser
- 2024
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Ingår i: Science Advances. - 2375-2548. ; 10:16, s. 0668-0668
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Tidskriftsartikel (refereegranskat)abstract
- Quantum entanglement between the degrees of freedom encountered in the classical world is challenging to observe due to the surrounding environment. To elucidate this issue, we investigate the entanglement generated over ultrafast timescales in a bipartite quantum system comprising two massive particles: a free-moving photoelectron, which expands to a mesoscopic length scale, and a light-dressed atomic ion, which represents a hybrid state of light and matter. Although the photoelectron spectra are measured classically, the entanglement allows us to reveal information about the dressed-state dynamics of the ion and the femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observed generation of entanglement is interpreted using the time-dependent von Neumann entropy. Our results unveil the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying spooky action at a distance.
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| 24. |
- Nandi, Saikat, et al.
(författare)
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Generation of entanglement using a short-wavelength seeded free-electron laser
- 2024
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Ingår i: SCIENCE ADVANCES. - 2375-2548. ; 10:16
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum entanglement between the degrees of freedom encountered in the classical world is challenging to observe due to the surrounding environment. To elucidate this issue, we investigate the entanglement generated over ultrafast timescales in a bipartite quantum system comprising two massive particles: a free-moving photoelectron, which expands to a mesoscopic length scale, and a light-dressed atomic ion, which represents a hybrid state of light and matter. Although the photoelectron spectra are measured classically, the entanglement allows us to reveal information about the dressed-state dynamics of the ion and the femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observed generation of entanglement is interpreted using the time-dependent von Neumann entropy. Our results unveil the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying spooky action at a distance.
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| 25. |
- Nandi, Saikat, et al.
(författare)
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Unraveling Rabi dynamics with a seeded FEL at XUV wavelength
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2023. - 9798350345995
-
Konferensbidrag (refereegranskat)abstract
- Rabi oscillations, a prominent feature of coherent light-matter interaction arise when a two-level system interacts periodically with an external electromagnetic field [1]. Despite being a cornerstone in quantum physics, they are usually studied in the long-wavelength region, ranging from mid-infrared to visible. Here, we demonstrate that intense femtosecond extreme-ultraviolet (XUV) pulses from FERMI seeded free-electron laser [2] can drive Rabi oscillations between the two levels: 1s2 and 1s4p in helium.
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| 26. |
- Ristea, Nicolae-Catalin, et al.
(författare)
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CyTran: A cycle-consistent transformer with multi-level consistency for non-contrast to contrast CT translation
- 2023
-
Ingår i: Neurocomputing. - : ELSEVIER. - 0925-2312 .- 1872-8286. ; 538
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Tidskriftsartikel (refereegranskat)abstract
- We propose a novel approach to translate unpaired contrast computed tomography (CT) scans to noncontrast CT scans and the other way around. Solving this task has two important applications: (i) to automatically generate contrast CT scans for patients for whom injecting contrast substance is not an option, and (ii) to enhance the alignment between contrast and non-contrast CT by reducing the differences induced by the contrast substance before registration.Our approach is based on cycle-consistent generative adversarial convolutional transformers, for short, CyTran. Our neural model can be trained on unpaired images, due to the integration of a multi-level cycleconsistency loss. Aside from the standard cycle-consistency loss applied at the image level, we propose to apply additional cycle-consistency losses between intermediate feature representations, which enforces the model to be cycle-consistent at multiple representations levels, leading to superior results. To deal with high-resolution images, we design a hybrid architecture based on convolutional and multi-head attention layers. In addition, we introduce a novel data set, Coltea-Lung-CT-100W, containing 100 3D triphasic lung CT scans (with a total of 37,290 images) collected from 100 female patients (there is one examination per patient). Each scan contains three phases (non-contrast, early portal venous, and late arterial), allowing us to perform experiments to compare our novel approach with state-of-the-art methods for image style transfer.Our empirical results show that CyTran outperforms all competing methods. Moreover, we show that CyTran can be employed as a preliminary step to improve a state-of-the-art medical image alignment method. We release our novel model and data set as open source at: https://github.com/ristea/cycletransformer.Our qualitative and subjective human evaluations reveal that CyTran is the only approach that does not introduce visual artifacts during the translation process. We believe this is a key advantage in our application domain, where medical images need to precisely represent the scanned body parts. (c) 2023 Elsevier B.V. All rights reserved.
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| 27. |
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| 28. |
- Ryding, Mauritz J., et al.
(författare)
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X-ray induced fragmentation of size-selected salt cluster-ions stored in an ion trap
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:88, s. 47743-47751
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Tidskriftsartikel (refereegranskat)abstract
- A method for spectroscopic characterization of free ionic clusters and nanoparticles utilizing X-ray synchrotron radiation is presented. We demonstrate that size-selected ammonium bisulphate cluster ions, NH4+(NH4HSO4)(n), captured in a linear ion trap, exhibit well-defined core-level absorption edges in the reconstructed fragment-ion abundance spectra. In addition to the specific photo-fragmentation pathways observed at the N1s-, O1s- and S2p-edges, dissociation also occurs as a consequence of clusters colliding with helium present as buffer gas in the ion trap. Separate off-beam experiments were conducted to establish the activation kinetics of these collision induced dissociation processes. Furthermore, it is demonstrated that the electrons released upon photoionization of background helium are too few in number to produce multiply charged cluster ions, and thereby induce fragmentation of the salt clusters, to any significant degree. The mechanisms for photon absorption and subsequent cluster fragmentation are analysed and discussed. In addition to its inherent element specificity, the method holds promise for cluster structure elucidation resulting from the sensitivity of the near edge absorption structure to the local chemical environment of the excited atom.
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| 29. |
- Söderström, Johan, 1978-, et al.
(författare)
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Angle-resolved electron spectroscopy of the resonant Auger decay in xenon with meV energy resolution
- 2011
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13, s. 073014-
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Tidskriftsartikel (refereegranskat)abstract
- The angle-resolved resonant Auger spectrum of Xe is investigated with a record high meV energy resolution in the kinetic energy region of 34.45-39.20 eV at hv = 65.110 eV, corresponding to the resonant excitation of the Auger Xe* 4d(5/2)(-1)6p state. New lines have been observed and assigned in the spectra. The results of previous measurements concerning energies, intensities and angular distribution asymmetry parameters have been refined, complemented and, for some of the lines, corrected.
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| 30. |
- Travnikova, Oksana, et al.
(författare)
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Circularly Polarized X Rays : Another Probe of Ultrafast Molecular Decay Dynamics
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:23
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Tidskriftsartikel (refereegranskat)abstract
- Dissociative nuclear motion in core-excited molecular states leads to a splitting of the fragment Auger lines: the Auger-Doppler effect. We present here for the first time experimental evidence for an Auger-Doppler effect following F1s -> a(1g)* inner-shell excitation by circularly polarized x rays in SF6. In spite of a uniform distribution of the dissociating S-F bonds near the polarization plane of the light, the intersection between the subpopulation of molecules selected by the core excitation with the cone of dissociation induces a strong anisotropy in the distribution of the S-F bonds that contributes to the scattering profile measured in the polarization plane.
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| 31. |
- Travnikova, Oksana, et al.
(författare)
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On Routes to Ultrafast Dissociation of Polyatomic Molecules
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:14, s. 2361-2366
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Tidskriftsartikel (refereegranskat)abstract
- Dissociation pathways for complex polyatomic molecules can sometimes be obscure due to the multitude of degrees of freedom involved. Here, we suggest the description of a dissociation mechanism implying multimode dynamics on the barrierless potential energy surface. The mechanism is elaborated from the X-ray spectroscopic analysis of the ultrafast nuclear motion in core?shell excited molecules. We infer that in large molecules, dissociation pathways are observed to deviate from the two-body dissociation coordinate due to the internal motion of light linkages, which alters dissociation rates and may yield heavy products on very short time scales. The mechanism is exemplified with the case of 1-bromo-2-chloroethane, where the rotation of the C2H4-moiety leads to the dissociation of C?Cl or C?Br bonds in Cl2p or Br3d core-excited states, whose lifetimes last only ?7 fs. Dissociation pathways for complex polyatomic molecules can sometimes be obscure due to the multitude of degrees of freedom involved. Here, we suggest the description of a dissociation mechanism implying multimode dynamics on the barrierless potential energy surface. The mechanism is elaborated from the X-ray spectroscopic analysis of the ultrafast nuclear motion in core?shell excited molecules. We infer that in large molecules, dissociation pathways are observed to deviate from the two-body dissociation coordinate due to the internal motion of light linkages, which alters dissociation rates and may yield heavy products on very short time scales. The mechanism is exemplified with the case of 1-bromo-2-chloroethane, where the rotation of the C2H4-moiety leads to the dissociation of C?Cl or C?Br bonds in Cl2p or Br3d core-excited states, whose lifetimes last only ?7 fs.
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| 32. |
- Travnikova, Oksana, et al.
(författare)
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The ESCA molecule-Historical remarks and new results
- 2012
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- The C is photoelectron spectrum of ethyl trifluoroacetate (CF3-CO-O-CH2-CH3), also known as the 'ESCA molecule', is the most illustrative showcase of chemical shifts in photoelectron spectroscopy. The binding energies of the four carbon atoms of this molecule spread over more than 8 eV with energy separations ranging from 1.7 to 3.1 eV owing to different chemical environments and hence different charge states of these atoms. The paper discusses history and importance of this spectrum in the field of photoelectron spectroscopy starting from the time of invention of the ESCA technique. The main focus of the paper is a 'revisit' of this spectrum using the most modern experimental and computational tools. Large geometrical changes, different for each ionization site, and the presence of two conformers of ethyl trifluoroacetate influence the spectral lineshapes of all four C 1s lines. These effects are carefully modeled by theory and investigated in the experimental spectrum.
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| 33. |
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