| 1. |
- Aad, G., et al.
(author)
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- 2011
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Journal article (peer-reviewed)
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| 2. |
- Åsman, Barbro, et al.
(author)
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The ATLAS Level-1 Calorimeter Trigger : PreProcessor implementation and performance
- 2012
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In: Journal of Instrumentation. - 1748-0221. ; 7
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Journal article (peer-reviewed)abstract
- The PreProcessor system of the ATLAS Level-1 Calorimeter Trigger (L1Calo) receives about 7200 analogue signals from the electromagnetic and hadronic components of the calorimetric detector system. Lateral division results in cells which are pre-summed to so-called Trigger Towers of size 0.1 x 0.1 along azimuth (phi) and pseudorapidity (eta). The received calorimeter signals represent deposits of transverse energy. The system consists of 124 individual PreProcessor modules that digitise the input signals for each LHC collision, and provide energy and timing information to the digital processors of the L1Calo system, which identify physics objects forming much of the basis for the full ATLAS first level trigger decision. This paper describes the architecture of the PreProcessor, its hardware realisation, functionality, and performance.
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| 3. |
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| 4. |
- Öberg, Henrik, et al.
(author)
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Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser : DFT prediction and X-ray confirmation of a precursor state
- 2015
-
In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 640, s. 80-88
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Journal article (peer-reviewed)abstract
- We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (<100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of similar to 2000K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (similar to 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate.
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| 5. |
- Born, A., et al.
(author)
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The degree of electron itinerancy and shell closing in the core-ionized state of transition metals probed by Auger-photoelectron coincidence spectroscopy
- 2022
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:32, s. 19218-19222
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Journal article (peer-reviewed)abstract
- Auger-photoelectron coincidence spectroscopy (APECS) has been used to examine the electron correlation and itinerance effects in transition metals Cu, Ni and Co. It is shown that the LVV Auger, in coincidence with 2p photoelectrons, spectra can be represented using atomic multiplet positions if the 3d-shell is localized (atomic-like) and with a self-convoluted valence band for band-like (itinerant) materials as explained using the Cini-Sawatzky model. For transition metals, the 3d band changes from band-like to localized with increasing atomic number, with the possibility of a mixed behavior. Our result shows that the LVV spectra of Cu can be represented by atomic multiplet calculations, those of Co resemble the self-convolution of the valence band and those of Ni are a mixture of both, consistent with the Cini-Sawatzky model.
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| 6. |
- Hennies, F., et al.
(author)
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Dynamic interpretation of resonant x-ray Raman scattering : ethylene and benzene
- 2007
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 76:3, s. 032505-
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Journal article (peer-reviewed)abstract
- We present a dynamic interpretation of resonant x-ray Raman scattering where vibrationally selective excitation into molecular resonances has been employed in comparison with excitation into higher lying continuum states for condensed ethylene and benzene as molecular model systems. In order to describe the purely vibrational spectral loss features and coupled electronic and vibrational losses the one-step theory for resonant soft x-ray scattering is applied, taking multiple vibrational modes and vibronic coupling into account. The scattering profile is found to be strongly excitation energy dependent and to reflect the intermediate states dynamics of the scattering process. In particular, the purely vibrational loss features allow one to map the electronic ground state potential energy surface in light of the excited state dynamics. Our study of ethylene and benzene underlines the necessity of an explicit description of the coupled electronic and vibrational loss features for the assignment of spectral features observed in resonant x-ray Raman scattering at polyatomic systems, which can be done in both a time independent and a time dependent picture. The possibility to probe ground state vibrational properties opens a perspective to future applications of this photon-in-photon-out spectroscopy.
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| 7. |
- Hennies, F., et al.
(author)
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Non-Adiabatic effects in Resonant Inelastic x-ray Scattering
- 2005
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 95:16, s. 163002-
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Journal article (peer-reviewed)abstract
- We have studied the spectral features of resonant inelastic x-ray scattering of condensed ethylene with vibrational selectivity both experimentally and theoretically. Purely vibrational spectral loss features and coupled electronic and vibrational losses are observed. The one-step theory for resonant soft x-ray scattering is applied, taking multiple vibrational modes and vibronic coupling into account. Our investigation of ethylene underlines that the assignment of spectral features observed in resonant inelastic x-ray scattering of polyatomic systems requires an explicit description of the coupled electronic and vibrational loss features.
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| 8. |
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| 9. |
- Leitner, Torsten, 1979-, et al.
(author)
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The CoESCA station at BESSY: Auger electron–photoelectron coincidences from surfaces demonstrated for Ag MNN
- 2021
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 250
-
Journal article (peer-reviewed)abstract
- In this work, we present the CoESCA station for electron–electron coincidence spectroscopy from surfaces, built in a close collaboration between Uppsala University and Helmholtz-Zentrum Berlin at the BESSY II synchrotron facility in Berlin, Germany. We start with a detailed overview of previous work in the field of electron–electron coincidences, before we describe the CoESCA setup and its design parameters. The system is capable of recording shot-to-shot resolved 6D coincidence datasets, i.e. the kinetic energy and the two take off angles for both coincident electrons. The mathematics behind extracting and analysing these multi-dimensional coincidence datasets is introduced, with a focus on coincidence statistics, resulting in fundamental limits of the signal-to-noise ratio and its implications for acquisition times and the size of the raw data stream. The functionality of the CoESCA station is demonstrated for the example of Auger electron–photoelectron coincidences from silver surfaces for photoelectrons from the Ag 3d core levels and their corresponding MNN Auger electrons. The Auger spectra originating from the different core levels, 3d and 3d could be separated and further, the two-hole state energy distributions were determined for these Auger decay channels.
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| 10. |
- Magnuson, Martin, et al.
(author)
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Resonant Auger spectroscopy at the L2,3 shake-up thresholds as a probe of electron correlation effects in nickel
- 1998
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 58:7, s. 3677-3681
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Journal article (peer-reviewed)abstract
- The excitation energy dependence of the three-hole satellites in the L3-M45M45 and L2-M45M45 Auger spectra of nickel metal has been measured using synchrotron radiation. The satellite behavior in the nonradiative emission spectra at the L3 and L2 thresholds is compared and the influence of the Coster-Kronig channel explored. The three-hole satellite intensity at the L3 Auger emission line reveals a peak structure at 5 eV above the L3 threshold attributed to resonant processes at the 2p53d9 shake-up threshold. This is discussed in connection with the 6-eV feature in the x-ray-absorption spectrum.
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| 11. |
- Magnuson, Martin, et al.
(author)
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X-ray fluorescence spectra of metals excited below threshold
- 2003
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:4
-
Journal article (peer-reviewed)abstract
- X-ray scattering spectra of Cu and Ni metals have been measured using monochromatic synchrotron radiation tuned from far above to more than 10 eV below threshold. Energy conservation in the scattering process is found to be sufficient to explain the modulation of the spectral shape, neglecting momentum conservation and channel interference. At excitation energies close to and above threshold, the emission spectra map the occupied local partial density of states. For the subthreshold excitations, the high-energy flank of the inelastic scattering exhibits a Raman-type linear dispersion, and an asymmetric low-energy tail develops. For excitation far below threshold the emission spectra are proportional to a convolution of the occupied and unoccupied local partial densities of states.
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| 12. |
- Pietzsch, A, et al.
(author)
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Snapshots of the Fluctuating Hydrogen Bond Network in Liquid Water on the Sub-Femtosecond Timescale with Vibrational Resonant Inelastic x-ray Scattering.
- 2015
-
In: Physical Review Letters. - 1079-7114. ; 114:8
-
Journal article (peer-reviewed)abstract
- Liquid water molecules interact strongly with each other, forming a fluctuating hydrogen bond network and thereby giving rise to the anomalous phase diagram of liquid water. Consequently, symmetric and asymmetric water molecules have been found in the picosecond time average with IR and optical Raman spectroscopy. With subnatural linewidth resonant inelastic x-ray scattering (RIXS) at vibrational resolution, we take sub-femtosecond snapshots of the electronic and structural properties of water molecules in the hydrogen bond network. We derive a strong dominance of nonsymmetric molecules in liquid water in contrast to the gas phase on the sub-femtosecond timescale of RIXS and determine the fraction of highly asymmetrically distorted molecules.
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| 13. |
- Rubensson, Jan-Erik, et al.
(author)
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Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds
- 2015
-
In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 114:13
-
Journal article (peer-reviewed)abstract
- Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.
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| 14. |
- Weinelt, M., et al.
(author)
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Resonant Photoemission at the 2p Edges of Ni: Resonant Raman and Interference Effects
- 1997
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 78:5, s. 967-970
-
Journal article (peer-reviewed)abstract
- Unambiguous evidence for resonant photoemission in Ni is presented. Interference effects are identified at the 2p edges for the valence band and the 6 eV satellite. A rapid transition from a resonant Raman to an Auger-like regime shows that the core-excited states above threshold are not localized enough to significantly enhance the photoemission intensity, implying a large fraction of incoherent intensity. The results indicate that the appearance of interference effects does not require strong localization of the intermediate state.
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| 15. |
- Öström, Henrik, et al.
(author)
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Ethylene on Cu(110) and Ni(110) : Electronic structure and bonding derived from x-ray spectroscopy and theory
- 2004
-
In: Surface Science. - : Elsevier. - 0039-6028. ; 559:2-3, s. 85-93
-
Journal article (peer-reviewed)abstract
- The bonding of ethylene to Cu(1 1 0) and Ni(1 1 0) is analyzed in detail using symmetry-resolved X-ray absorption (XAS) and emission (XES) spectroscopies in conjunction with density functional theory (DFT) calculations of geometric structure and spectra. XES, which probes the occupied valence states, reveals the formation of bonding and non-bonding orbitals of π-3d as well as π*-3d character. Additional mixing of σ and π states indicates rehybridization upon adsorption. The anti-bonding π-3d and π*-3d combinations are unoccupied and seen in XAS. A lower intensity of the π* transition for Ni is evidence of larger π* occupancy upon bonding. The position of the σ* shape-resonance indicates a 0.02 Å longer C–C bond on Ni than on Cu, in good agreement with the DFT structure optimizations. The XE spectra are well-reproduced both by specific spectrum calculations based on cluster models and by the carbon p-density of states calculated using periodic boundary conditions. The contribution of both π and π* levels to the new, surface-induced occupied states close to the Fermi-level lends support to the traditional Dewar–Chatt–Duncanson picture of the bonding. Theoretical charge-density difference plots support an alternative view of ethylene bonding in terms of the specific involvement of the excited molecular triplet state. Based on the variation in XE intensities the main difference between ethylene bonding to Cu and Ni is found to be an about two times larger occupancy of the π* orbital upon chemisorption on the transition metal, which comes along with C–C bond elongation and stronger σ–π rehybridization.
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| 16. |
- Jay, Raphael M., et al.
(author)
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Disentangling Transient Charge Density and Metal-Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering
- 2018
-
In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:12, s. 3538-3543
-
Journal article (peer-reviewed)abstract
- Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. pi-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences sigma-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.
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| 17. |
- Kunnus, K., et al.
(author)
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Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)(5) to Fe(CO)(4)EtOH
- 2016
-
In: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 3:4
-
Journal article (peer-reviewed)abstract
- We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)(5) in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)(4) which are observed following a charge transfer photoexcitation of Fe(CO)(5) as reported in our previous study [ Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the (1)A(1) state of Fe(CO)(4). A sub-picosecond time constant of the spin crossover from B-1(2) to B-3(2) is rationalized by the proposed B-1(2) -> (1)A(1) -> B-3(2) mechanism. Ultrafast ligation of the B-1(2) Fe(CO)(4) state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the B-3(2) Fe(CO)(4) ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via B-1(2) -> (1)A(1) -> (1)A'Fe(CO)(4)EtOH pathway and the time scale of the (1)A(1) Fe(CO)(4) state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution.
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| 18. |
- Kunnus, K., et al.
(author)
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Quantifying covalent interactions with resonant inelastic soft X-ray scattering : Case study of Ni2+ aqua complex
- 2017
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 669, s. 196-201
-
Journal article (peer-reviewed)abstract
- We analyze the effects of covalent interactions in Ni 2p3d resonant inelastic X-ray scattering (RIXS) spectra from aqueous Ni2+ ions and find that the relative RIXS intensities of ligand-to-metal charge-transfer final states with respect to the ligand-field final states reflect the covalent mixing between Ni 3d and water orbitals. Specifically, the experimental intensity ratio at the Ni L-3-edge allows to determine that the Ni 3d orbitals have on average 5.5% of water character. We propose that 2p3d RIXS at the Ni L-3-edge can be utilized to quantify covalency in Ni complexes without the use of external references or simulations.
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| 19. |
- Liu, J. -C, et al.
(author)
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Time-resolved study of recoil-induced rotation by X-ray pump - X-ray probe spectroscopy
- 2022
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:11, s. 6627-6638
-
Journal article (peer-reviewed)abstract
- Modern stationary X-ray spectroscopy is unable to resolve rotational structure. In the present paper, we propose to use time-resolved two color X-ray pump-probe spectroscopy with picosecond resolution for real-time monitoring of the rotational dynamics induced by the recoil effect. The proposed technique consists of two steps. The first short pump X-ray pulse ionizes the valence electron, which transfers angular momentum to the molecule. The second time-delayed short probe X-ray pulse resonantly excites a 1s electron to the created valence hole. Due to the recoil-induced angular momentum the molecule rotates and changes the orientation of transition dipole moment of core-excitation with respect to the transition dipole moment of the valence ionization, which results in a temporal modulation of the probe X-ray absorption as a function of the delay time between the pulses. We developed an accurate theory of the X-ray pump-probe spectroscopy of the recoil-induced rotation and study how the energy of the photoelectron and thermal dephasing affect the structure of the time-dependent X-ray absorption using the CO molecule as a case-study. We also discuss the feasibility of experimental observation of our theoretical findings, opening new perspectives in studies of molecular rotational dynamics.
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| 20. |
- Norell, Jesper, et al.
(author)
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Ab initio simulations of complementary K-edges and solvatization effects for detection of proton transfer in aqueous 2-thiopyridone
- 2019
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:11
-
Journal article (peer-reviewed)abstract
- The nitrogen and sulfur K-edge X-ray absorption spectra of aqueous 2-thiopyridone, a model system for excited-state proton transfer in several recent time-resolved measurements, have been simulated from ab initio molecular dynamics. Spectral signatures of the local intra- and inter-molecular structure are identified and rationalized, which facilitates experimental interpretation and optimization. In particular, comparison of aqueous and gas phase spectrum simulations assesses the previously unquantified solvatization effects, where hydrogen bonding is found to yield solvatochromatic shifts up to nearly 1 eV of the main peak positions. Thereby, while each K-edge can still decisively determine the local protonation of its core-excited site, only their combined, complementary fingerprints allow separating all of the three relevant molecular forms, giving a complete picture of the proton transfer.
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| 21. |
- Pietzsch, Annette, et al.
(author)
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Spatial Quantum Beats in Vibrational Resonant Inelastic Soft X-Ray Scattering at Dissociating States in Oxygen
- 2011
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 106, s. 153004-153008
-
Journal article (peer-reviewed)abstract
- Resonant inelastic soft x-ray scattering (RIXS) spectra excited at the 1σg→3σu resonance in gas-phase O2 show excitations due to the nuclear degrees of freedom with up to 35 well-resolved discrete vibronic states and a continuum due to the kinetic energy distribution of the separated atoms. The RIXS profile demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the atoms separate. Thomson scattering strongly affects both the spectral profile and the scattering anisotropy.
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| 22. |
- Sun, Yuping, et al.
(author)
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Intramolecular soft modes and intermolecular interactions in liquid acetone
- 2011
-
In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 84:13
-
Journal article (peer-reviewed)abstract
- Resonant inelastic x-ray scattering spectra excited at the O1s−1π* resonance of liquid acetone are presented. Scattering to the electronic ground state shows a resolved vibrational progression where the dominant contribution is due to the C-O stretching mode, thus demonstrating a unique sensitivity of the method to the local potential energy surface in complex molecular systems. For scattering to electronically excited states, soft vibrational modes and, to a smaller extent, intermolecular interactions give a broadening, which blurs the vibrational fine structure. It is predicted that environmental broadening is dominant in aqueous acetone.
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| 23. |
- Wernet, Ph., et al.
(author)
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Communication : Direct evidence for sequential dissociation of gas-phase Fe(CO)(5) via a singlet pathway upon excitation at 266 nm
- 2017
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 146:21
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Journal article (peer-reviewed)abstract
- We prove the hitherto hypothesized sequential dissociation of Fe(CO)(5) in the gas phase upon photoexcitation at 266 nm via a singlet pathway with time-resolved valence and core-level photoelectron spectroscopy with an x-ray free-electron laser. Valence photoelectron spectra are used to identify free CO molecules and to determine the time constants of stepwise dissociation to Fe(CO)(4) within the temporal resolution of the experiment and further to Fe(CO)(3) within 3 ps. Fe 3p core-level photoelectron spectra directly reflect the singlet spin state of the Fe center in Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3) showing that the dissociation exclusively occurs along a singlet pathway without triplet-state contribution. Our results are important for assessing intra- and intermolecular relaxation processes in the photodissociation dynamics of the prototypical Fe(CO)(5) complex in the gas phase and in solution, and they establish time-resolved core-level photoelectron spectroscopy as a powerful tool for determining the multiplicity of transition metals in photochemical reactions of coordination complexes.
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