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- ItemA 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, FranziskaMechanical 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.
- ItemCovalency-Driven Preservation of Local Charge Densities in a Metal-to-Ligand Charge-Transfer Excited Iron Photosensitizer(Weinheim : Wiley-VCH, 2019) Jay, Raphael M.; Eckert, Sebastian; Vaz da Cruz, Vinicius; Fondell, Mattis; Mitzner, Rolf; Föhlisch, AlexanderCovalency is found to even out charge separation after photo-oxidation of the metal center in the metal-to-ligand charge-transfer state of an iron photosensitizer. The σ-donation ability of the ligands compensates for the loss of iron 3d electronic charge, thereby upholding the initial metal charge density and preserving the local noble-gas configuration. These findings are enabled through element-specific and orbital-selective time-resolved X-ray absorption spectroscopy at the iron L-edge. Thus, valence orbital populations around the central metal are directly accessible. In conjunction with density functional theory we conclude that the picture of a localized charge-separation is inadequate. However, the unpaired spin density provides a suitable representation of the electron–hole pair associated with the electron-transfer process. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemGraphene Q-switched Yb:KYW planar waveguide laser(New York, NY : American Inst. of Physics, 2015) Kim, Jun Wan; Young Choi, Sun; Aravazhi, Shanmugam; Pollnau, Markus; Griebner, Uwe; Petrov, Valentin; Bae, Sukang; Jun Ahn, Kwang; Yeom, Dong-Il; Rotermund, FabianA diode-pumped Yb:KYW planar waveguide laser, single-mode Q-switched by evanescent-field interaction with graphene, is demonstrated for the first time. Few-layer graphene grown by chemical vapor deposition is transferred onto the top of a guiding layer, which initiates stable Q-switched operation in a 2.4-cm-long waveguide laser operating near 1027 nm. Average output powers up to 34 mW and pulse durations as short as 349 ns are achieved. The measured output beam profile, clearly exhibiting a single mode, agrees well with the theoretically calculated mode intensity distribution inside the waveguide. As the pump power is increased, the repetition rate and pulse energy increase from 191 to 607 kHz and from 7.4 to 58.6 nJ, respectively, whereas the pulse duration decreases from 2.09 μs to 349 ns.
- ItemInfrared spectroscopy in superfluid helium droplets(Abingdon : Taylor and Francis Ltd., 2019) Verma D.; Tanyag R.M.P.; O’Connell S.M.O.; Vilesov A.F.For more than two decades, encapsulation in superfluid helium nanodroplets has served as a reliable technique for probing the structure and dynamics of molecules and clusters at a low temperature of ≈0.37 K. Due to weak interactions between molecules and the host liquid helium, good spectral resolution can usually be achieved, making helium droplets an ideal matrix for spectroscopy in a wide spectral range from infrared to ultraviolet. Furthermore, rotational structure in the spectra of small molecules provides a unique probe for interactions with the superfluid on an atomic scale. This review presents a summary of results and a discussion of recent experimental developments in helium droplet spectroscopy with the emphasis laid on infrared studies. Initially, studies focused on single molecules and have been expanded to larger species, such as metal-molecular clusters, biomolecules, free radicals, ions, and proteins. © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
- ItemProperties of LiGa0.5In0.5Se2: A Quaternary Chalcogenide Crystal for Nonlinear Optical Applications in the Mid-IR(Basel : MDPI, 2016) Isaenko, Ludmila; Yelisseyev, Alexander; Lobanov, Sergei; Vedenyapin, Vitaliy; Krinitsyn, Pavel; Petrov, ValentinLiGaSe2 (LGSe) and LiInSe2 (LISe) are wide band-gap nonlinear crystals transparent in the mid-IR spectral range. LiGa0.5In0.5Se2 (LGISe) is a new mixed crystal, a solid solution in the system LGSe–LISe, which exhibits the same orthorhombic structure (mm2) as the parent compounds in the same time being more technological with regard to the growth process. In comparison with LGSe and LISe its homogeneity range is broader in the phase diagram. About 10% of the Li ions in LGISe occupy octahedral positions (octapores) with coordination number of 3. The band-gap of LGISe is estimated to be 2.94 eV at room temperature and 3.04 eV at 80 K. The transparency at the 0-level extends from 0.47 to 13 µm. LGISe crystals exhibit luminescence in broad bands centered near 1.7 and 1.25 eV which is excited most effectively by band-to-band transition. From the measured principal refractive indices and the fitted Sellmeier equations second-harmonic generation from 1.75 to 11.8 μm (fundamental wavelength) is predicted. The nonlinear coefficients of LGISe have values between those of LGSe and LISe. 6LGISe crystals are considered promising also for detection of thermal neutrons.
- ItemWater Dynamics in the Hydration Shells of Biomolecules(Washington, DC : ACS Publ., 2017) Laage, Damien; Elsaesser, Thomas; Hynes, James T.The structure and function of biomolecules are strongly influenced by their hydration shells. Structural fluctuations and molecular excitations of hydrating water molecules cover a broad range in space and time, from individual water molecules to larger pools and from femtosecond to microsecond time scales. Recent progress in theory and molecular dynamics simulations as well as in ultrafast vibrational spectroscopy has led to new and detailed insight into fluctuations of water structure, elementary water motions, electric fields at hydrated biointerfaces, and processes of vibrational relaxation and energy dissipation. Here, we review recent advances in both theory and experiment, focusing on hydrated DNA, proteins, and phospholipids, and compare dynamics in the hydration shells to bulk water.
- 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.
- ItemXUV double-pulses with femtosecond to 650 ps separation from a multilayer-mirror-based split-and-delay unit at FLASH(Chester : IUCr, 2018-8-3) Sauppe, Mario; Rompotis, Dimitrios; Erk, Benjamin; Bari, Sadia; Bischoff, Tobias; Boll, Rebecca; Bomme, Cédric; Bostedt, Christoph; Dörner, Simon; Düsterer, Stefan; Feigl, Torsten; Flückiger, Leonie; Gorkhover, Tais; Kolatzki, Katharina; Langbehn, Bruno; Monserud, Nils; Müller, Erland; Müller, Jan P.; Passow, Christopher; Ramm, Daniel; Rolles, Daniel; Schubert, Kaja; Schwob, Lucas; Senfftleben, Björn; Treusch, Rolf; Ulmer, Anatoli; Weigelt, Holger; Zimbalski, Jannis; Zimmermann, Julian; Möller, Thomas; Rupp, DanielaExtreme ultraviolet (XUV) and X-ray free-electron lasers enable new scientific opportunities. Their ultra-intense coherent femtosecond pulses give unprecedented access to the structure of undepositable nanoscale objects and to transient states of highly excited matter. In order to probe the ultrafast complex light-induced dynamics on the relevant time scales, the multi-purpose end-station CAMP at the free-electron laser FLASH has been complemented by the novel multilayer-mirror-based split-and-delay unit DESC (DElay Stage for CAMP) for time-resolved experiments. XUV double-pulses with delays adjustable from zero femtoseconds up to 650 picoseconds are generated by reflecting under near-normal incidence, exceeding the time range accessible with existing XUV split-and-delay units. Procedures to establish temporal and spatial overlap of the two pulses in CAMP are presented, with emphasis on the optimization of the spatial overlap at long time-delays via time-dependent features, for example in ion spectra of atomic clusters.
- ItemExcited-state relaxation of hydrated thymine and thymidine measured by liquid-jet photoelectron spectroscopy: experiment and simulation(Washington, DC : ACS Publications, 2015) Buchner, Franziska; Nakayama, Akira; Yamazaki, Shohei; Ritze, Hans-Hermann; Lübcke, AndreaTime-resolved photoelectron spectroscopy is performed on thymine and thymidine in aqueous solution to study the excited-state relaxation dynamics of these molecules. We find two contributions with sub-ps lifetimes in line with recent excited-state QM/MM molecular dynamics simulations (J. Chem. Phys.2013, 139, 214304). The temporal evolution of ionization energies for the excited ππ* state along the QM/MM molecular dynamics trajectories were calculated and are compatible with experimental results, where the two contributions correspond to the relaxation paths in the ππ* state involving different conical intersections with the ground state. Theoretical calculations also show that ionization from the nπ* state is possible at the given photon energies, but we have not found any experimental indication for signal from the nπ* state. In contrast to currently accepted relaxation mechanisms, we suggest that the nπ* state is not involved in the relaxation process of thymine in aqueous solution.
- ItemCAMP@FLASH: an end-station for imaging, electron- and ion-spectroscopy, and pump–probe experiments at the FLASH free-electron laser(Chester : IUCr, 2018-8-2) Erk, Benjamin; Müller, Jan P.; Bomme, Cédric; Boll, Rebecca; Brenner, Günter; Chapman, Henry N.; Correa, Jonathan; Düsterer, Stefan; Dziarzhytski, Siarhei; Eisebitt, Stefan; Graafsma, Heinz; Grunewald, Sören; Gumprecht, Lars; Hartmann, Robert; Hauser, Günter; Keitel, Barbara; von Korff Schmising, Clemens; Kuhlmann, Marion; Manschwetus, Bastian; Mercadier, Laurent; Müller, Erland; Passow, Christopher; Plönjes, Elke; Ramm, Daniel; Rompotis, Dimitrios; Rudenko, Artem; Rupp, Daniela; Sauppe, Mario; Siewert, Frank; Schlosser, Dieter; Strüder, Lothar; Swiderski, Angad; Techert, Simone; Tiedtke, Kai; Tilp, Thomas; Treusch, Rolf; Schlichting, Ilme; Ullrich, Joachim; Moshammer, Robert; Möller, Thomas; Rolles, DanielThe non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump–probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, along with large-area single-photon-counting pnCCD X-ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end-station are presented, as well as results from its commissioning.