97 research outputs found
Surface analysis of the PrB6 (001) cleavage plane by scanning tunneling microscopy and spectroscopy
No full textScanning tunneling microscopy and spectroscopy were performed on the (001) cleavage plane of praseodymium hexaboride (PrB6). We found three different ordered morphologies, namely, a chainlike (2 × 1) reconstruction and two uniform terminations. The chainlike (2 × 1) reconstruction is rationalized as parallel Pr rows on top of a complete B6 network. The two uniform terminations are identified as complete Pr or B6 layers. Although the uniform terminations could be expected to be simply (1 × 1) reconstructed, one of them shows a rather stripelike atomic corrugation for close tip-sample distances. All morphologies share two spectral features at −0.2 and +0.2 eV around EF. In addition, one uniform termination shows an additional peak in the differential conductance at −0.7 eV. Similarly, the chainlike (2 × 1) reconstruction reveals a feature in the differential conductance at −1.1 eV when moving the tip closer to the surface. The distance dependency points towards rather localized electronic states, which we tentatively attribute to a 4 f -related feature
SIGN CHANGES IN THE ELECTRIC DIPOLE MOMENT OF EXCITED STATES IN RUBIDIUM-ALKALINE EARTH DIATOMIC MOLECULES
No full textIn a recent series of combined experimental and theoretical studies we investigated the ground state and several excited states of the Rb-alkaline earth molecules RbSrfootnote{F. Lackner, G. Krois, T. Buchsteiner, J. V. Pototschnig, and W. E. Ernst, Phys. Rev. Lett., 2014, 113, 153001; G. Krois, F. Lackner, J. V. Pototschnig, T. Buchsteiner, and W. E. Ernst, Phys. Chem. Chem. Phys., 2014, 16, 22373; J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Chem. Phys., 2014, 141, 234309} and RbCa.footnote{J. V. Pototschnig, G. Krois, F. Lackner, and W. E. Ernst, J. Mol. Spectrosc., in Press (2015), doi:10.1016/j.jms.2015.01.006} The group of alkali-alkaline earth (AK-AKE) molecules has drawn attention for applications in ultracold molecular physics and the measurement of fundamental constantsfootnote{M. Kajita, G. Gopakumar, M. Abe, and M. Hada, J. Mol. Spectrosc., 2014, 300, 99-107} due to their large permanent electric and magnetic dipole moments in the ground state. These properties should allow for an easy manipulation of the molecules and simulations of spin models in optical lattices.footnote{A. Micheli, G. K. Brennen, and P. Zoller, Nature Physics, 2006, 2, 341-347}
In our studies we found that the permanent electric dipole moment points in different directions for certain electronically excited states, and changes the sign in some cases as a function of bond length. We summarize our results, give possible causes for the measured trends in terms of molecular orbital theory and extrapolate the tendencies to other combinations of AK and AKE - elements.Made available in DSpace on 2016-01-05T20:03:32Z (GMT). No. of bitstreams: 3
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Previous issue date: 2
Molecular spectra of RbSr: Helium droplet assisted preparation of a diatomic molecule
No full textWe report on the first spectroscopic investigation of the ground and excited states of RbSr. The molecules are prepared in their vibronic ground state () in a sequential pickup process\footnote{G. Krois, J.V. Pototschnig, F. Lackner and W.E. Ernst, J. Phys. Chem. A, 117 (50), 13719-13731 (2013)} on the surface of helium nanodroplets, confined in a cold (0.38\,K) and weakly perturbing superfluid environment\footnote{C.~Callegari and W.~E.~Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M.~Quack and F.~Merkt, John Wiley \& Sons, Chichester, (2011)}. Utilizing resonance-enhanced multi-photon ionization time-of-flight (REMPI-TOF) spectroscopy and laser induced fluorescence (LIF) spectroscopy our investigations cover the spectral regime of 11500\,cm\,-\,23000\,cm. The weak interaction between molecules and helium droplets causes a broadening of the observed transitions. For spectrally resolved band systems the helium droplet isolation approach facilitates the determination of molecular constants. Our assignment is assisted by theoretical calculations of potential energy curves based on a multireference configuration interaction (MRCI) approach. Several strong transitions could be identified; the most prominent spectral feature is a vibrational resolved band system at 14000\,cm. In contrast to the excitation spectra, dispersed fluorescence (DF) spectra are not influenced by the helium environment, because the molecules leave the droplets upon photoexcitation, revealing detailed insights into the electronic structure of the free RbSr molecule. \\
Our experiments will aid the ongoing search for optimal pathways for the preparation of ultracold ground state RbSr molecules\footnote{P.S. {\.Z}uchowski, R. Guerout, and O. Dulieu, arXiv preprint arXiv:1402.0702 (2014)}\footnote{B. Pasquiou, A. Bayerle, S.M. Tzanova, S. Stellmer, J. Szczepkowski, M. Parigger, R. Grimm, and F. Schreck, Phys. Rev. A, 88 (2), 023601 (2013)}.Made available in DSpace on 2014-09-17T16:55:01Z (GMT). No. of bitstreams: 3
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Previous issue date: 2014-06-19Made available in DSpace on 2015-04-14T18:40:49Z (GMT). No. of bitstreams: 4
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Previous issue date: 2014-06-1
Surface resonance of the (2×1) reconstructed lanthanum hexaboride (001)-cleavage plane : a combined STM and DFT study
No full textWe performed a combined study of the (001)-cleavage plane of lanthanum hexaboride (LaB6) using scanning tunneling microscopy and density-functional theory (DFT). Experimentally, we found a (2×1) reconstructed surface on a local scale. The reconstruction is only short-range ordered and tends to order perpendicularly to step edges. At larger distances from surface steps, the reconstruction evolves to a labyrinthlike pattern. These findings are supported by low-energy electron diffraction experiments. Slab calculations within the framework of DFT show that the atomic structure consists of parallel lanthanum chains on top of boron octahedra. Scanning tunneling spectroscopy shows a prominent spectral feature at −0.6eV. Using DFT, we identify this structure as a surface resonance of the (2×1) reconstructed LaB6 (100) surface which is dominated by boron dangling bond states and lanthanum d states
Quasielastic neutron scattering experiments including activation energies and mathematical modeling of methyl halide dynamics
No full textQuasielastic neutron scattering experiments were carried out using the multichopper time-of-flight spectrometer V3 at the Hahn-Meitner Institut, Germany and the backscattering spectrometer at Forschungszentrum Julich, Germany. Activation energies for CH(3)X, X=F, Cl, Br, and I, were obtained. In combination with results from previous inelastic neutron scattering experiments the data were taken to describe the dynamics of the halides in terms of two different models, the single particle model and the coupling model. Coupled motions of methyl groups seem to explain the dynamics of the methyl fluoride and chloride; however, the coupling vanishes with the increase of the mass of the halide atom in CH(3)Br and CH(3)I
International Journal of Mathematical Combinatorics, Vol.4A
No full textThe International J.Mathematical Combinatorics (ISSN 1937-1055) is a fully refereed international journal, sponsored by the MADIS of Chinese Academy of Sciences and published in USA quarterly comprising 460 pages approx. per volume, which publishes original research papers and survey articles in all aspects of Smarandache multi-spaces, Smarandache geometries, mathematical combinatorics, non-euclidean geometry and topology and their applications to other sciences
Dynamics in biological membranes from neutron scattering and dielectric spectroscopy experiments
No full textWe report dielectric spectroscopy DS results from temperature T and hydration h dependent measurements on multi layer stacks of purple membrane PM . The frequency dependent dielectric permittivity conveys dynamic information, since it images electric dipole motions. In the investigated range of the physical parameters 235 K lt; T lt; 275 K, 0.23 wt H2O lt; h lt; 0.47 wt H2O, 10 3 amp; 8804; f amp; 8804; 10 6 Hz , the dielectric permittivity of PM stacks, their lamellar lattice constant and the quasielastic incoherent structure factors QISFs exhibit a qualitatively very similar behavior as a function of T and h. A supercooling effect with a freezing discontinuity at the temperature Tfh and a continuous increase of the dielectric permittivity upon reheating, with a melting discontinuity point Tmh gt; Tfh, were observed. The variation of Tmh as a function of water content resembles very much the neutron result, except for a systematic difference due to the use of H2O for DS rather than D2O for neutrons as solvent. The existence of crystalline ice at temperatures below 245 K, known from neutron diffraction, has now been demonstrated by dielectric spectroscopy as well. The imaginary part of the frequency dependent dielectric function exhibits two relaxation peaks at low temperature e.g., f 800 Hz and 25000 Hz, at 223 K , while at higher temperatures the dielectric spectrum is conductivity dominated, showing no relaxation peaks. All in all, we demonstrate the extremely useful complementarity of dielectric spectroscopy and neutron scattering, both working in different frequency regime
]: Convenient Syntheses and Computational Analysis of Strikingly Dissimilar Siblings
No full text[Rh2(MEPY)4] is a versatile catalyst for asymmetric synthesis but its preparation requires purification by chromatography on surface‐modified silica. A higher yielding procedure based on a more convenient work‐up is presented herein. Likewise, a much improved method for the preparation of [BiRh(OTfa)4] is described, which makes this heterobimetallic complex readily available. Subsequent exchange of the trifluoroacetate ligands opens access to a so far underappreciated family of (chiral) paddlewheel complexes. While [BiRh] complexes comprising four carboxylate ligands are highly adequate for intermolecular asymmetric cyclopropanation reactions, [BiRh(MEPY)4] as the heterobimetallic cousin of [Rh2(MEPY)4] was found to be surprisingly unreactive; DFT calculations uncover the reasons for this inertia
Hydrogen cycling behavior of LiBD4 Al studied by in situ neutron diffraction
No full textThe preparation of Li11BD4 from Al11B2, LiD and D2 and several subsequent hydrogen sorption cycles according to 2LiD AlB2 3D2 amp; 8596; 2LiBD4 Al starting from the desorbed state are investigated by in situ neutron diffraction. Absorption is carried out at T 450 amp; 9702; C and at p 50 bar D2, while desorption is performed at T 450 amp; 9702; C using a back pressure of 1 bar. Compared to the Al free system, the absorption is observed at much lower temperatures and pressures.We attribute the increased deuterium uptake to the enhanced chemical reactivity of the elemental boron released in the dissociation of AlB2. The desorption process on the other hand is similar to the desorption of pure LiBD4 and seems not to be influenced by the present aluminum. The hydrogen capacity decreases from cycle to cycle, due to an incomplete re formation of AlB2. We attribute this to a phase separation of Al and B during the decomposition of LiBD
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