| | 44 | Author
| F. Gasser, M. Roeth | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0257.pdf | | | | Identifier
| ZNA-1993-48a-0257 | | | | Volume
| 48 | |
| 47 | Author
| F. Bell, Th Tschentscher, J. R. Schneider, A. J. Rollason | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0273.pdf | | | | Identifier
| ZNA-1993-48a-0273 | | | | Volume
| 48 | |
| 48 | Author
| J. R. Schmitz, H. Schulte-Schrepping, A. Berthold, S. Mourikis, W. Schülke | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0279.pdf | | | | Identifier
| ZNA-1993-48a-0279 | | | | Volume
| 48 | |
| 49 | Author
| A. Berthold, K.-J Gabriel, W. Schülke | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0283.pdf | | | | Identifier
| ZNA-1993-48a-0283 | | | | Volume
| 48 | |
| 50 | Author
| E. Burkel | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0289.pdf | | | | Identifier
| ZNA-1993-48a-0289 | | | | Volume
| 48 | |
| 51 | Author
| S. Manninen, V. Honkimäki, P. Suortti | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0295.pdf | | | | Identifier
| ZNA-1993-48a-0295 | | | | Volume
| 48 | |
| 53 | Author
| Tanja Asthalter, Wolf Weyrich | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0303.pdf | | | | Identifier
| ZNA-1993-48a-0303 | | | | Volume
| 48 | |
| 55 | Author
| M. Weisser, W. Weyrich | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0315.pdf | | | | Identifier
| ZNA-1993-48a-0315 | | | | Volume
| 48 | |
| 56 | Author
| R. O. Horenian, W. Weyrich | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0325.pdf | | | | Identifier
| ZNA-1993-48a-0325 | | | | Volume
| 48 | |
| 57 | Author
| B. K. Sharma | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0334.pdf | | | | Identifier
| ZNA-1993-48a-0334 | | | | Volume
| 48 | |
| 58 | Author
| D. N. Timms, M. J. Cooper | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0343.pdf | | | | Identifier
| ZNA-1993-48a-0343 | | | | Volume
| 48 | |
| 59 | Author
| Usha Mittal, B. K. Sharma, R. K. Kothari, B. L. Ahuja | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0348.pdf | | | | Identifier
| ZNA-1993-48a-0348 | | | | Volume
| 48 | |
| 60 | Author
| Wolfgang Schütz, Beate Waldeck, Dietmar Flösch, Wolf Weyrich | Requires 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 | | | |
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| default:Reihe_A/48/ZNA-1993-48a-0352.pdf | | | | Identifier
| ZNA-1993-48a-0352 | | | | Volume
| 48 | |
|
