Search Results

Now showing 1 - 10 of 412
  • Item
    Ultrafast inter-ionic charge transfer of transition-metal complexes mapped by femtosecond x-ray powder diffraction
    (Les Ulis : EDP Sciences, 2013) Zamponi, F.; Freyer, B.; Juvé, V.; Stingl, J.; Woerner, M.; Chergui, M.; Elsaesser, T.
    Transient electron density maps are derived from x-ray diffraction patterns of photoexcited [Fe(bpy)3]2+(PF6 -)2 powder. Upon photoexcitation, the 5T 2 quintet state reveals a charge transfer from the PF 6- ions and from the Fe atoms to neighboring bpy units. The charge transfer from the Fe points to a partial and weak charge-transfer character of this state.
  • Item
    Application of Matched-Filter Concepts to Unbiased Selection of Data in Pump-Probe Experiments with Free Electron Lasers
    (Basel : MDPI, 2017-06-16) Callegari, Carlo; Takanashi, Tsukasa; Fukuzawa, Hironobu; Motomura, Koji; Iablonskyi, Denys; Kumagai, Yoshiaki; Mondal, Subhendu; Tachibana, Tetsuya; Nagaya, Kiyonobu; Nishiyama, Toshiyuki; Matsunami, Kenji; Johnsson, Per; Piseri, Paolo; Sansone, Giuseppe; Dubrouil, Antoine; Reduzzi, Maurizio; Carpeggiani, Paolo; Vozzi, Caterina; Devetta, Michele; Faccialà, Davide; Calegari, Francesca; Castrovilli, Mattea; Coreno, Marcello; Alagia, Michele; Schütte, Bernd; Berrah, Nora; Plekan, Oksana; Finetti, Paola; Ferrari, Eugenio; Prince, Kevin; Ueda, Kiyoshi
    Pump-probe experiments are commonly used at Free Electron Lasers (FEL) to elucidate the femtosecond dynamics of atoms, molecules, clusters, liquids and solids. Maximizing the signal-to-noise ratio of the measurements is often a primary need of the experiment, and the aggregation of repeated, rapid, scans of the pump-probe delay is preferable to a single long-lasting scan. The limited availability of beamtime makes it impractical to repeat measurements indiscriminately, and the large, rapid flow of single-shot data that need to be processed and aggregated into a dataset, makes it difficult to assess the quality of a measurement in real time. In post-analysis it is then necessary to devise unbiased criteria to select or reject datasets, and to assign the weight with which they enter the analysis. One such case was the measurement of the lifetime of Intermolecular Coulombic Decay in the weakly-bound neon dimer. We report on the method we used to accomplish this goal for the pump-probe delay scans that constitute the core of the measurement; namely we report on the use of simple auto- and cross-correlation techniques based on the general concept of “matched filter”. We are able to unambiguously assess the signal-to-noise ratio (SNR) of each scan, which then becomes the weight with which a scan enters the average of multiple scans. We also observe a clear gap in the values of SNR, and we discard all the scans below a SNR of 0.45. We are able to generate an average delay scan profile, suitable for further analysis: in our previous work we used it for comparison with theory. Here we argue that the method is sufficiently simple and devoid of human action to be applicable not only in post-analysis, but also for the real-time assessment of the quality of a dataset.
  • Item
    A Mechanistic Perspective on Plastically Flexible Coordination Polymers
    (Weinheim : Wiley-VCH, 2019) Bhattacharya, Biswajit; Michalchuk, Adam A.L.; Silbernagl, Dorothee; Rautenberg, Max; Schmid, Thomas; Feiler, Torvid; Reimann, Klaus; Ghalgaoui, Ahmed; Sturm, Heinz; Paulus, Beate; Emmerling, Franziska
    Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one-dimensional (1D) coordination polymer. The compound [Zn(μ-Cl)2(3,5-dichloropyridine)2]n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
  • Item
    Phonon driven charge dynamics in polycrystalline acetylsalicylic acid mapped by ultrafast x-ray diffraction
    (Melville, NY : AIP Publishing LLC, 2019) Hauf, Christoph; Hernandez Salvador, Antonio-Andres; Holtz, Marcel; Woerner, Michael; Elsaesser, Thomas
    The coupled lattice and charge dynamics induced by phonon excitation in polycrystalline acetylsalicylic acid (aspirin) are mapped by femtosecond x-ray powder diffraction. The hybrid-mode character of the 0.9 ± 0.1 THz methyl rotation in the aspirin molecules is evident from collective charge relocations over distances of some 100 pm, much larger than the sub-picometer nuclear displacements. Oscillatory charge relocations around the methyl group generate a torque on the latter, thus coupling electronic and nuclear motions.
  • Item
    Forscherverbund: German Israeli cooperation in ultrafast laser technologies (GILCULT) : Projekt: Femtosecond coherent control for nonlinear spectroscopy ; Abschlußbericht
    (Hannover : Technische Informationsbibliothek (TIB), 2004) Korn, G.; Silberberg, Yaron; Zhavoronkov, Nikolay; Laarmann, Tim
    [no abstract available]
  • Item
    Signatures of attosecond electronic–nuclear dynamics in the one-photon ionization of molecular hydrogen: analytical model versusab initiocalculations
    ([London] : IOP, 2015) Medišauskas, Lukas; Morales, Felipe; Palacios, Alicia; González-Castrillo, Alberto; Plimak, Lev; Smirnova, Olga; Martín, Fernando; Ivanov, Misha Yu
    We present an analytical model based on the time-dependent WKB approximation to reproduce the photoionization spectra of an H2 molecule in the autoionization region. We explore the nondissociative channel, which is the major contribution after one-photon absorption, and we focus on the features arising in the energy differential spectra due to the interference between the direct and the autoionization pathways. These features depend on both the timescale of the electronic decay of the autoionizing state and the time evolution of the vibrational wavepacket created in this state. With full ab initio calculations and with a one-dimensional approach that only takes into account the nuclear wavepacket associated to the few relevant electronic states we compare the ground state, the autoionizing state, and the background continuum electronic states. Finally, we illustrate how these features transform from molecular-like to atomic-like by increasing the mass of the system, thus making the electronic decay time shorter than the nuclear wavepacket motion associated with the resonant state. In other words, autoionization then occurs faster than the molecular dissociation into neutrals.
  • Item
    Probing multiphoton light-induced molecular potentials
    ([London] : Nature Publishing Group UK, 2020) Kübel, M.; Spanner, M.; Dube, Z.; Naumov, A.Yu.; Chelkowski, S.; Bandrauk, A.D.; Vrakking, M.J.J.; Corkum, P.B.; Villeneuve, D.M.; Staudte, A.
    The strong coupling between intense laser fields and valence electrons in molecules causes distortions of the potential energy hypersurfaces which determine the motion of the nuclei and influence possible reaction pathways. The coupling strength varies with the angle between the light electric field and valence orbital, and thereby adds another dimension to the effective molecular potential energy surface, leading to the emergence of light-induced conical intersections. Here, we demonstrate that multiphoton couplings can give rise to complex light-induced potential energy surfaces that govern molecular behavior. In the laser-induced dissociation of H2+, the simplest of molecules, we measure a strongly modulated angular distribution of protons which has escaped prior observation. Using two-color Floquet theory, we show that the modulations result from ultrafast dynamics on light-induced molecular potentials. These potentials are shaped by the amplitude, duration and phase of the dressing fields, allowing for manipulating the dissociation dynamics of small molecules.
  • Item
    Preparation of clay mineral samples for high resolution x-ray imaging
    (Bristol : Institute of Physics Publishing, 2013) Abbati, G.; Seim, C.; Legall, H.; Stiel, H.; Thomas, N.; Wilhein, T.
    In the development of optimum ceramic materials for plastic forming, it is of fundamental importance to gain insight into the compositions of the clay minerals. Whereas spectroscopic methods are adequate for determining the elemental composition of a given sample, a knowledge of the spatial composition, together with the shape and size of the particles leads to further, valuable insight. This requires an imaging technique such as high resolution X-ray microscopy. In addition, fluorescence spectroscopy provides a viable element mapping technique. Since the fine particle fraction of the materials has a major effect on physical properties like plasticity, the analysis is focused mainly on the smallest particles. To separate these from the bigger agglomerates, the raw material has to pass through several procedures like centrifugation and filtering. After that, one has to deposit a layer of appropriate thickness on to a suitable substrate. These preparative techniques are described here, starting from the clay mineral raw materials and proceeding through to samples that are ready to analyze. First results using high resolution x-ray imaging are shown.
  • Item
    Differential Cross Sections for the H + D2 → HD(v′ = 3, j′ = 4-10) + D Reaction above the Conical Intersection
    (Washington, DC : Soc., 2015) Gao, Hong; Sneha, Mahima; Bouakline, Foudhil; Althorpe, Stuart C.; Zare, Richard N.
    We report rovibrationally selected differential cross sections (DCSs) of the benchmark reaction H + D2 → HD(v′ = 3, j′ = 4–10) + D at a collision energy of 3.26 eV, which exceeds the conical intersection of the H3 potential energy surface at 2.74 eV. We use the PHOTOLOC technique in which a fluorine excimer laser at 157.64 nm photodissociates hydrogen bromide (HBr) molecules to generate fast H atoms and the HD product is detected in a state-specific manner by resonance-enhanced multiphoton ionization. Fully converged quantum wave packet calculations were performed for this reaction at this high collision energy without inclusion of the geometric phase (GP) effect, which takes into account coupling to the first excited state of the H3 potential energy surface. Multimodal structures can be observed in most of the DCSs up to j′ = 10, which is predicted by theory and also well-reproduced by experiment. The theoretically calculated DCSs are in good overall agreement with the experimental measurements, which indicates that the GP effect is not large enough that its existence can be verified experimentally at this collision energy.
  • Item
    Excitation of H2 at large internuclear separation: F1∑+g outer well states and continuum resonances
    (London : Taylor & Francis, 2019) Trivikram, T.M.; Salumbides, E.J.; Jungen, Ch.; Ubachs, W.
    Bound and free quantum resonances of molecular hydrogen exhibiting wave-function density at large internuclear separation, (Formula presented.) 4–5 a.u., are excited via multi-step laser spectroscopy. Highly excited vibrational levels of H (Formula presented.) are prepared via two-photon UV-photolysis of H (Formula presented.) S. Subsequent two-photon Doppler-free precision measurements are performed connecting (Formula presented.) levels with (Formula presented.) outer-well levels. Detection and spectroscopic labelling of the quantum states is assisted by further laser excitation into the auto-ionisation continuum employing a third UV-laser. Level energies of high rotational states ((Formula presented.)) in the outer-well state (Formula presented.) are accurately determined. The three-laser study demonstrates a method for probing resonances in the H (Formula presented.) ionisation continuum with wave-function density at large internuclear separation (Formula presented.) 4–5 a.u., large angular momenta J, and energy range 131,100–133,000 cm-1, a hitherto unexplored territory. © 2019, © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.