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- ItemUltrafast 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.
- ItemPhonon 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, ThomasThe 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.
- ItemForscherverbund: 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]
- ItemSignatures of attosecond electronic–nuclear dynamics in the one-photon ionization of molecular hydrogen: analytical model versusab initiocalculations([London] : IOP, 2015) MediÅ¡auskas, Lukas; Morales, Felipe; Palacios, Alicia; González-Castrillo, Alberto; Plimak, Lev; Smirnova, Olga; MartÃn, Fernando; Ivanov, Misha YuWe 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.
- ItemPreparation 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.
- ItemDifferential 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.
- ItemExcitation 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.
- ItemPlasma rotation with circularly polarized laser pulse(London : Hindawi, 2015) Lécz, Z.; Andreev, A.; Seryi, A.The efficient transfer of angular orbital momentum from circularly polarized laser pulses into ions of solid density targets is investigated with different geometries using particle-in-cell simulations. The detailed electron and ion dynamics presented focus upon the energy and momentum conversion efficiency. It is found that the momentum transfer is more efficient for spiral targets and the maximum value is obtained when the spiral step is equal to twice the laser wavelength. This study reveals that the angular momentum distribution of ions strongly depends up on the initial target shape and density.
- ItemUltrafast two-dimensional THz spectroscopy of graphene(Les Ulis : EDP Sciences, 2013) Bowlan, P.; Martinez Moreno, E.; Reimann, K.; Woerner, M.; Elsaesser, T.With two-dimensional THz spectroscopy the dynamics of low-energy carriers in graphene is determined. Both intra- and interband absorption contribute to the observed ultrafast pump-probe signals.
- ItemUltrafast Structural Changes in Chiral Molecules Measured with Free-Electron Lasers(Bristol : IOP Publ., 2020) Schmidt, P.; Music, V.; Hartmann, G.; Boll, R.; Erk, B.; Bari, S.; Allum, F.; Baumann, T.M.; Brenner, G.; Brouard, M.; Burt, M.; Coffee, R.; Dörner, S.; Galler, A.; Grychtol, P.; Heathcote, D.; Inhester, L.; Kazemi, M.; Larsson, M.; Li, Z.; Lutmann, A.; Manschwetus, B.; Marder, L.; Mason, R.; Moeller, S.; Osipov, T.; Otto, H.; Passow, C.; Rolles, D.; Rupprecht, P.; Schubert, K.; Schwob, L.; Thomas, R.; Vallance, C.; Von Korff Schmising, C.; Wagner, R.; Walter, P.; Wolf, T.J.A.; Zhaunerchyk, V.; Meyer, M.; Ehresmann, A.; Knie, A.; Demekhin, P.V.; Ilchen, M.(X-ray) free-electron lasers are employed to site specifically interrogate atomic fragments during ultra-fast photolysis of chiral molecules via time-resolved photoelectron circular dichroism. © 2020 Institute of Physics Publishing. All rights reserved.