Go toArchive
Browse byFacets
Bookbag ( 0 )
Facet   Publication Year 1993  [X]
Results  635 Items
Sorted by   
Section
Publication Year
1993[X]
41Author    Alejandro Saenz, Wolf WeyrichRequires cookie*
 Title    The Generalised Oscillator-Strength Density of the Helium Atom, Calculated by a New Implementation of the Complex-Coordinate Method  
 Abstract    We report a calculation of the generalised oscillator-strength density (GOSD) of the helium atom for low momentum transfer. The calculation was performed by extraction of the searched entity from the resolvent of the complex-rotated Hamiltonian. That Hamiltonian was found using a standard ab-initio program without any change in the program code. The shape of the Bethe surface is reproduced (including resonances and the absorption edge). However, with increasing momentum transfer the magnitude of the calculated values for the Bethe ridge becomes too small. This is clearly demonstrated by an evaluation of the Bethe sum as a function of the momentum transfer. A comparison with recent additional theoretical data shows that the deviations are due to the em-ployed basis set. 
  Reference    Z. Naturforsch. 48a, 243—250 (1993); received April 25 1992 
  Published    1993 
  Keywords    Generalised oscillator-strength density, Complex scaling, Bethe surface, Ab-initio cal-culation, Inelastic scattering 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0243.pdf 
 Identifier    ZNA-1993-48a-0243 
 Volume    48 
42Author    C. TavardRequires cookie*
 Title    Double-Ionisation Processes and Electronic Structures  
 Abstract    The electron momentum distribution of a given target can be extracted, under impulsive condi-tions, from the simple ionisation processes relevant to Compton collisions. This document classifies and investigates the physical mechanisms of double ionisation, in connection with the target elec-tronic structure. 
  Reference    Z. Naturforsch. 48a, 251—254 (1993); received October 17 1991 
  Published    1993 
  Keywords    Double-ionisation processes, Scattering cross-section, Electron scattering, inelastic, Electronic structure 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0251.pdf 
 Identifier    ZNA-1993-48a-0251 
 Volume    48 
43Author    B. Joulakian, C. DalRequires cookie*
 Title    The Effect of Correlation on the Double Ionization of Helium by Fast Electrons  
 Abstract    The double ionization of helium by fast electrons is studied by using a correlated double con-tinuum wave function describing the two ejected electrons. 
  Reference    Z. Naturforsch. 48a, 255—256 (1993); received October 17 1991 
  Published    1993 
  Keywords    Double-ionisation processes, Scattering cross-section, Electron scattering, inelastic, Electron correlation 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0255.pdf 
 Identifier    ZNA-1993-48a-0255 
 Volume    48 
44Author    F. Gasser, M. RoethRequires cookie*
 Title    Compton Profiles for Atoms and Molecules: Compton Defects  
 Abstract    A series expansion applied to the Born propagator present in the differential cross-section allows one to obtain successive corrections to the impulse approximation. The first and second corrections explain the essential features of the Compton defects. Results for the second corrective term are presented for 1 s, 2 s, 2 p x , and 2 p z hydrogenic states. The decrease or increase of the scattered intensity near the maximum of the Compton profile is shown to be strongly related to geometric properties of the concerned orbital 
  Reference    Z. Naturforsch. 48a, 257—260 (1993); received December 24 1991 
  Published    1993 
  Keywords    Electronic structure, Ionisation cross-section, Compton scattering 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0257.pdf 
 Identifier    ZNA-1993-48a-0257 
 Volume    48 
45Author    StephenW. LoveseyRequires cookie*
 Title    Theories of Compton Scattering by Magnetic Materials  
 Abstract    Theoretical work on the cross-section for Compton scattering by magnetic materials is surveyed. Exact results for scattering by a free polarized electron are contrasted with corresponding results obtained perturbatively for a model of bound electrons with a finite width to the momentum distribution. 
  Reference    Z. Naturforsch. 48a, 261—265 (1993); received December 14 1991 
  Published    1993 
  Keywords    Compton scattering, Scattering cross-section, Magnetic materials, Spin density in momentum space 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0261.pdf 
 Identifier    ZNA-1993-48a-0261 
 Volume    48 
46Author    L. DobrzyńskiRequires cookie*
 Title    Recent Advances in Compton Scattering  
 Abstract    A review of achievements in the field of Compton spectrometry in the years that elapsed from the last Sagamore meeting (1988) is presented. Some physical problems that have either appeared as new or became clarified are described. Special emphasis is put to the results obtained by means of magnetic Compton scattering. 
  Reference    Z. Naturforsch. 48a, 266—272 (1993); received January 9 1992 
  Published    1993 
  Keywords    Compton scattering, Electron momentum distribution, Synchrotron radiation, Mag-netic materials 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0266.pdf 
 Identifier    ZNA-1993-48a-0266 
 Volume    48 
47Author    F. Bell, Th Tschentscher, J. R. Schneider, A. J. RollasonRequires cookie*
 Title    Electron Momentum Densities by (y, e y)-Spectroscopy  
 Abstract    We report coincidence measurements of inelastically scattered 148 keV photons and the recoil electrons generated within thin Al and Cu foils. We have analyzed both the Doppler broadening of the scattered photon intensity and the angular correlation of the recoil electron. This corresponds to different scans through the three-dimensional electron momentum density of the target. Estimates of the triple-differential cross-section for Compton scattering are given. The experiment was per-formed with synchrotron radiation from a bending magnet of the DORIS storage ring at DESY, Hamburg. 
  Reference    Z. Naturforsch. 48a, 273—278 (1993); received October 8 1991 
  Published    1993 
  Keywords    Electron momentum densities, Compton scattering, Synchrotron radiation 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0273.pdf 
 Identifier    ZNA-1993-48a-0273 
 Volume    48 
48Author    J. R. Schmitz, H. Schulte-Schrepping, A. Berthold, S. Mourikis, W. SchülkeRequires cookie*
 Title    Performance of the Compton Spectrometer at HARWI/HASYLAB  
 Abstract    Performance, resolution and spectral throughput both of the sagittally focusing monochromator and of the alternately installed two analysing systems, a Cauchois-type cylindrically bent crystal analyser for Compton-profile measurements, and a spherically bent crystal analyser for S(q, (^-mea-surements, of the new Compton spectrometer at the HARWI (harter Röntgen Wiggler) of the DORIS storage ring are presented together with two typical applications. 
  Reference    Z. Naturforsch. 48a, 279—282 (1993); received December 24 1991 
  Published    1993 
  Keywords    X-ray spectrometer, Inelastic X-ray scattering, Focusing X-ray optics, Compton pro-file, Dynamic structure factor 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0279.pdf 
 Identifier    ZNA-1993-48a-0279 
 Volume    48 
49Author    A. Berthold, K.-J Gabriel, W. SchülkeRequires cookie*
 Title    The Dynamic Structure Factor of LiC 6 and KC 8 : Inelastic Synchrotron X-Ray Scattering Results  
 Abstract    The dynamic structure factor S(q, &>) of electrons in lithium-intercalated graphite (LiC 6) and potassium-intercalated graphite (KC 8) for momentum transfer q || c-axis has been measured by inelastic synchrotron X-ray scattering. The dielectric function s{q, a>) was deduced from the data and compared with e(q, co) of pristine graphite. The main feature in the different Im [e(q, tt>)]-spectra, a more or less intense peak around 14 eV, can be assigned to maxima of the symmetry-projected joint density of occupied and unoccupied electron states near the Fermi level. Knowing the position of the occupied bands by photoemission experi-ments, predictions about the unoccupied n and interlayer states can be made. In the case of LiC 6 , a shift and broadening of the first Im [e(q, a>)]-peak was found, which can be explained by a decrease of the energy of the interlayer-band because of the strong hybridization of this graphite-derived band with the Li metal 2s-band. In the case of KC 8 , a weakening of the first peak of Im [e(q, co)] was observed, which we attribute both to a decreasing overlap of the occupied 7t-derived state with the empty interlayer state and to a change of symmetry of the occupied er-derived states as well as of the empty rc-derived states. 
  Reference    Z. Naturforsch. 48a, 283—288 (1993); received December 30 1991 
  Published    1993 
  Keywords    Inelastic X-ray scattering, Dynamic structure factor, Graphite, Graphite intercalation compounds, Interlayer state 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0283.pdf 
 Identifier    ZNA-1993-48a-0283 
 Volume    48 
50Author    E. BurkelRequires cookie*
 Title    Ultrahigh-Energy-Resolution Inelastic X-Ray Scattering Spectroscopy  
 Abstract    Very-high-energy-resolution measurements using X-rays can be achieved by extreme backreflec-tion (Bragg angle close to 90°) from perfect crystals. This technique allowed the development of the instrument INELAX for inelastic scattering experiments at the HARWI wiggler at DORIS, DESY Hamburg. Recently, a high energy resolution of 9 meV could be achieved, and the instrument proved to be an excellent tool to investigate collective excitations in condensed matter. Energy transfers from 10 meV to 12 eV and wave vectors up to about 10 Ä -1 are accessible. 
  Reference    Z. Naturforsch. 48a, 289—294 (1993); received January 8 1992 
  Published    1993 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0289.pdf 
 Identifier    ZNA-1993-48a-0289 
 Volume    48 
51Author    S. Manninen, V. Honkimäki, P. SuorttiRequires cookie*
 Title    Anisotropy of the Electron Momentum Distribution in Pyrolytic Graphite Studied Using a WK«! Spectrometer  
 Abstract    A new spectrometer construction based on a high-voltage W-anode x-ray tube has been used to measure the directional Compton profiles of a pyrolytic graphite crystal. Owing to the focusing geometry, the monochromatic WKa t beam is very well collimated, which improves the momentum resolution compared with conventional 241 Am spectrometers, operated almost at the same energy. The experimental anisotropy in the basal plane and in the direction of the c-axis is found to be very close to that of a recent calculation, based on the pseudopotential local-density-functional model. 
  Reference    Z. Naturforsch. 48a, 295—298 (1993); received December 12 1991 
  Published    1993 
  Keywords    Compton profile, Pyrolytic graphite, WKoq-spectrometer, Focusing monochromator, Autocorrelation function 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0295.pdf 
 Identifier    ZNA-1993-48a-0295 
 Volume    48 
52Author    D. L. Anastassopoulos, G. D. PriftisRequires cookie*
 Title    The Asymmetry of the Compton Profiles and its Dependence on the Geometrical Resolution  
 Abstract    The asymmetry of Compton Profiles (CPs) measured with a 60-keV 241 Am source on an Al monocrystal, cut along [111], is reported for three different geometrical resolutions. It is found that the geometry of the spectrometer has a substantial effect on the asymmetry of the CP. The better the geometrical resolution the smaller the asymmetry of the CPs. 
  Reference    Z. Naturforsch. 48a, 299—302 (1993); received December 19 1991 
  Published    1993 
  Keywords    Compton profile, Compton asymmetry, Geometrical resolution, Compton spectros-copy, y-ray spectroscopy 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0299.pdf 
 Identifier    ZNA-1993-48a-0299 
 Volume    48 
53Author    Tanja Asthalter, Wolf WeyrichRequires cookie*
 Title    The Anisotropy of the Reciprocal Form Factor and the Electronic Structure of Crystalline Lithium Hydride  
 Abstract    New high-precision measurements of the isotropic as well as of three directional Compton spectra of lithium hydride have been carried out using 24 'Am as a y-ray source. In order to account for the extreme sensitivity of LiH powder to atmospheric moisture, the final data (i.e. the reciprocal form factor) were corrected for the LiOH content determined by titrimetric analysis. For the interpreta-tion of the data, theoretical calculations were carried out using a Hartree-Fock program for periodic systems (CRYSTAL). Basis sets published by Dovesi et al. were used, one of which allows for polarisation of both the hydride and lithium ions. Comparison of the theoretical data with the experiment shows much better agreement of the results of complete solid-state calculations that take into account higher-order effects (polarisation and covalency) than those obtained by Löwdin orthogonalisation of free-ion wave functions (which assumes pure ionicity, neglecting all but first-order effects). The influence of further polarisation functions on the reciprocal form factor is inves-tigated and discussed. The remaining discrepancies are attributed to electron-electron correlation. 
  Reference    Z. Naturforsch. 48a, 303—309 (1993); received January 13 1993 
  Published    1993 
  Keywords    Compton spectroscopy, Reciprocal form factor, Ionic crystal, Electronic structure, Lithium hydride 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0303.pdf 
 Identifier    ZNA-1993-48a-0303 
 Volume    48 
54Author    B. L. Ahuja, Anil Gupta, B. K. SharmaRequires cookie*
 Title    Compton Profile of Boron Nitride  
 Abstract    The Compton profile of hexagonal boron nitride has been measured using 59.54 keV gamma rays and a planar Ge detector. The results are compared with theoretical Compton profiles calculated for various ionic arrangements and with those available from a bond orbital model, LCAO and SC canonical HF calculations. The LCAO calculation is in relatively good agreement with the present measurement. 
  Reference    Z. Naturforsch. 48a, 310—314 (1993); received December 31 1991 
  Published    1993 
  Keywords    Compton profile, Electron momentum distribution, Hartree-Fock calculation, Ionic model, Linear combination of atomic orbitals 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0310.pdf 
 Identifier    ZNA-1993-48a-0310 
 Volume    48 
55Author    M. Weisser, W. WeyrichRequires cookie*
 Title    The Electronic Structure of Hydrogen Bonding in a-Oxalic Acid Dihydrate  
 Abstract    Compton spectra of a-oxalic acid dihydrate single-crystal slices and powder samples were mea-sured in a helium atmosphere using 59.537 keV 241 Am radiation. In the anisotropic case, the scattering vector was oriented parallel to the shortest hydrogen bond, in the direction of the C = O bond, parallel to the C — O bond and perpendicular to the (a, c)-plane. The comparison of theoretical reciprocal form factors, calculated with a local density-approximation (LDA) method for an a-(COOH) 2 • 2H 2 0 cluster in triple-zeta basis-set quality, with the experimental data has demon-strated that there is a considerable influence of intermolecular interactions on the electronic struc-ture. Further calculations including the intermolecular interactions of the first coordination sphere by symmetrical orthogonalisation of the LDA wave functions clearly improved the agreement of experiment and theory. A theoretical analysis of the reciprocal form factor B a (s) in the direction of the three different hydrogen bonds of a-oxalic acid dihydrate on the basis of the cluster calculations has shown that in the region above s = 1.9 Ä all these bonds are dominated by electrostatic attrac-tion and exchange repulsion of the donor and the acceptor system. 
  Reference    Z. Naturforsch. 48a, 315—324 (1993); received January 28 1993 
  Published    1993 
  Keywords    a-Oxalic acid dihydrate, Compton spectroscopy, Hydrogen bonding, Reciprocal form factor, Density functional calculations 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0315.pdf 
 Identifier    ZNA-1993-48a-0315 
 Volume    48 
56Author    R. O. Horenian, W. WeyrichRequires cookie*
 Title    Momentum-Density Studies of Some Compounds with Triatomic Linear Anions  
 Abstract    High-purity powder samples of lithium and sodium azide (LiN 3 , NaN 3), cyanate (LiOCN, NaOCN) and hydrogen fluoride (LiFHF, NaFHF) were studied by means of 59.54 keV Compton spectroscopy. The measured isotropic Compton profiles were corrected for multiple scattering and transformed to spherically averaged reciprocal form factors B a (s). The experimental results are compared with theoretical reciprocal form factors obtained from Hartree-Fock calculations with different types of basis sets (Gaussian-and Slater-type orbitals, with and without polarisation functions) both for the free ions and for several kinds of clusters. The importance of intraionic and interionic interaction for the description of chemical bonding in these compounds is pointed out and discussed. 
  Reference    Z. Naturforsch. 48a, 325—333 (1993); received January 28 1993 
  Published    1993 
  Keywords    Compton spectroscopy, Azides, Hydrogen fluorides, Cyanates, Ionic crystals 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0325.pdf 
 Identifier    ZNA-1993-48a-0325 
 Volume    48 
57Author    B. K. SharmaRequires cookie*
 Title    Compton Scattering from Heavier Metals  
 Abstract    The use of Compton scattering in the determination of electronic structure has grown consider-ably in the last two decades. With the advent of synchrotron radiation it has become possible, even with good resolution, to measure several single-crystal orientations to determine three-dimensional electron momentum distributions. Although most of the earlier work has been directed to low-Z materials, in the last few years medium and high-Z metals have also been investigated with this technique. In this paper we present a review of these studies on heavier metals with particular attention to the difficulties encountered. Compton profile measurements from techniques based on energetic ion beams are also considered briefly. 
  Reference    Z. Naturforsch. 48a, 334—342 (1993); received December 31 1991 
  Published    1993 
  Keywords    Compton profiles, Electron momentum distributions, Electronic structure, Brems-strahlung, Ion Compton profile 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0334.pdf 
 Identifier    ZNA-1993-48a-0334 
 Volume    48 
58Author    D. N. Timms, M. J. CooperRequires cookie*
 Title    The Electron Momentum Distribution in Lead  
 Abstract    Directional Compton profiles have been measured along the [100], [110] and [111] crystallo-graphic axes in lead using 412 and 59.5 keV y-radiation from 98 Au and Am radioisotope sources, respectively. Both measurements are in mutual agreement and show a small anisotropy, which is just distinguishable within the statistical error. The spherically averaged data have been compared with the predictions of relativistic Hartree-Fock (RHF) and non-relativistic Hartree-Fock (HF) free atom calculations. As expected, the experiment clearly favours the RHF rather than the HF calculation. 
  Reference    Z. Naturforsch. 48a, 343—347 (1993); received January 11 1992 
  Published    1993 
  Keywords    Compton profile, Electron momentum distribution, Relative effects, Lead 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0343.pdf 
 Identifier    ZNA-1993-48a-0343 
 Volume    48 
59Author    Usha Mittal, B. K. Sharma, R. K. Kothari, B. L. AhujaRequires cookie*
 Title    Bremsstrahlung Contribution in Compton Scattering from Heavy Metals  
 Abstract    Theoretical estimates of the spectral distribution and total intensity of the bremsstrahlung (BS) relative to the Compton yield have been determined for photoelectrons liberated in scattering experiments on heavy metals with 60 keV radiation. Whereas the total-intensity calculations are based on the approach of Alexandropoulos et al., the spectral distribution has been computed using the Born approximation along with the Elwert and form factor corrections. These results are compared with another calculation based on the approach of Lee et al. Typical results for Mo, Ta, and W are presented. It is found that the relative contribution of BS from a W target is not trivially small, although K-shell photo-ionisation is not possible at these energies. 
  Reference    Z. Naturforsch. 48a, 348—351 (1993); received December 31 1991 
  Published    1993 
  Keywords    Compton profile, Bremsstrahlung, Born approximation, Photoelectrons, Screened potential 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0348.pdf 
 Identifier    ZNA-1993-48a-0348 
 Volume    48 
60Author    Wolfgang Schütz, Beate Waldeck, Dietmar Flösch, Wolf WeyrichRequires cookie*
 Title    Compton Scattering Experiments with Polychromatic Radiation  
 Abstract    We show an iterative algorithm that allows to obtain accurate Compton profiles J(q) from Compton scattering spectra / 2 (o> 2), if the excitation radiation is not strictly monochromatic. It requires knowledge of the spectral distribution of the primary radiation (coj, validity of the impulse approximation and dominance of a monochromatic part in (CD 1) over the polychromatic rest. Conversely, the primary spectrum is often experimentally not directly accessible. In such a situation it is possible to evaluate the primary spectrum ^(coj from the spectrum of scattered photons, / 2 (a> 2), w ith a similar iterative algorithm. We use a scattering target of high atomic number in order to ensure that the elastically scattered photons dominate the inelastically scattered ones. From the scattered spectrum we get a model for the Compton profile that allows us to separate the inelastic part of the scattered spectrum from the elastic part, which, in turn, is proportional to the spectral distribution of the primary radiation. 
  Reference    Z. Naturforsch. 48a, 352—357 (1993); reveived 
  Published    1993 
  Keywords    Compton spectroscopy, Polychromaticity, Scattering cross-section 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0352.pdf 
 Identifier    ZNA-1993-48a-0352 
 Volume    48 
Prev
1
2
3
4
5
...
Next