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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3809-3817 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A gas-phase time-of-flight (TOF) apparatus, capable of supporting as many as six electron-TOF analyzers viewing the same interaction region, has been developed to measure energy- and angle-resolved electrons with kinetic energies up to 5 keV. Each analyzer includes a newly designed lens system that can retard electrons to about 2% of their initial kinetic energy without significant loss of transmission; the analyzers can thus achieve a resolving power (E/ΔE) greater than 104 over a wide kinetic-energy range. Such high resolving power is comparable to the photon energy resolution of state-of-the-art synchrotron–radiation beamlines in the soft x-ray range, opening the TOF technique to numerous high-resolution applications. In addition, the angular placement of the analyzers, by design, permits detailed studies of nondipolar angular distribution effects in gas-phase photoemission. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1745-1747 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Beamline 9.3.1 at the Advanced Light Source (ALS) is a windowless beamline, covering the 1–6 keV photon-energy range, designed to achieve the goals of high energy resolution, high flux, and high brightness at the sample. When completed later this year, it will be the first ALS monochromatic hard-x-ray beamline, and its brightness will be an order-of-magnitude higher than presently available in this energy range. In addition, it will provide flux and resolution comparable to any other beamline now in operation. To achieve these goals, two technical improvements, relative to existing x-ray beamlines, were incorporated. First, a somewhat novel optical design for x rays, in which matched toroidal mirrors are positioned before and after the double-crystal monochromator, was adopted. This configuration allows for high resolution by passing a collimated beam through the monochromator, and for high brightness by focusing the ALS source on the sample with unit magnification. Second, a new "Cowan type'' double-crystal monochromator based on the design used at NSLS beamline X-24A was developed. The measured mechanical precision of this new monochromator shows significant improvement over existing designs, without using positional feedback available with piezoelectric devices. Such precision is essential because of the high brightness of the radiation and the long distance (12 m) from the source (sample) to the collimating (focusing) mirror. This combination of features will provide a bright, high resolution, and stable x-ray beam for use in the x-ray spectroscopy program at the ALS. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new "Cowan type'' double-crystal monochromator, based on the boomerang design used at National Synchrotron Light Source (NSLS) beamline X-24A, has been developed for beamline 9.3.1 at the Advanced Light Source (ALS), a windowless ultrahigh vacuum beamline covering the 1–6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design of the monochromator has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-23A2, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Beamline 9.3.1 at the Advanced Light Source (ALS) is a windowless beamline, covering the 1–6 keV photon energy range. This beamline is designed to achieve the goal of high brightness at the sample for use in the x-ray atomic and molecular spectroscopy (XAMS) science, surface and interface science, biology and x-ray optical development programs at ALS. X-ray absorption and time-of-flight photoemission measurements in 2–5 keV photon energy range along with the flux, resolution, spot size and stability of the beamline will be discussed. Prospects for future XAMS measurements will also be presented. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3255-3256 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relationship between shape−resonance energies and bond lengths within agiven molecule is explored further.It is contended that some shape−resonance assignments presented by Stohr and Hitchcock (ref.1) are not convincing.(AIP)
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2765-2771 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A discussion is presented on the general nature of shape resonances in small molecules and how they may relate to molecular bond lengths. Criteria for assigning photoabsorption features as shape resonances are described, and the usefulness of photoemission experiments to such assignments is highlighted. Based on these criteria, all unambiguously identified K-shell shape-resonance features in molecules containing B, C, N, O, and F are examined in an attempt to identify empirically a shape-resonance energy/bond length relationship. Although the available data are insufficient to establish a quantitative correlation, they indicate the influence of other variables besides the bond length to the energy position of a shape resonance.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3004-3009 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Resonant photoemission has been studied above the carbon 1s ionization thresholds in gas-phase benzene and ethylene. The experimental data for both molecules include relative partial cross section and asymmetry-parameter measurements for the C 1s main line and asymmetry-parameter measurements for one C 1s shake-up satellite in each system. Resonances above the C K edge have been analyzed on the basis of their decay to either the C 1s main line or valence-hole states, and have been tentatively assigned as either shape resonances or doubly excited states according to their observed one-electron or many-electron decay, respectively. The importance of determining the resonant behavior of all available photoemission channels in the proximity of a resonance is thus illustrated.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6096-6102 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Zero kinetic energy (ZKE) spectra of N2, CO, C2H4, and C6H6 were taken across the N1s (N2) and C1s ionization thresholds. Discrete resonances at subthreshold photon energies were observed and were found to become more intense as threshold is approached relative to the same peaks in absorption spectra. For N2 the satellite/main line branching ratios at threshold are: 11(1)% for the 419.7(1) eV binding energy satellite, and 2.3(1.0)% for the 426.5(1) eV binding energy satellite. For CO, the branching ratio for the 304.6(1) eV binding energy satellite is 15(2)% at its threshold. Branching ratios at threshold are also determined for the satellites of C6H6 and C2H4. Decay characteristics and assignments of the continuum features of C6H6 and C2H4 are also discussed.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4726-4736 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The core-level photoexcitation and photoionization of SF6 were studied in the vicinity of the resonances below and above the S 2p threshold. The decay channels of the S 2p→6a1g discrete excitation were characterized, with decay leading mostly to valence-shell satellites. The S 2p continuum data show an oscillatory asymmetry parameter β(S 2p) near threshold that is virtually identical to β(Si 2p) in SiF4. It also resembles—but differs from—theoretical curves for β(S 2p) in atomic sulfur and in SF6. Data at the feature assigned as an eg shape resonance indicate strong multielectron properties for this state, because a resonance in the S 2p satellite is observed at the same photon energy as the main-line resonance. We propose a unified model which generally includes configuration interaction both in the continuum-state manifold and between discrete doubly excited states and the continua, to explain this unexpected satellite behavior. Finally, the S(L2,3VV) Auger electron asymmetry parameter shows no significant deviation from zero near the t2g and eg shape resonances.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Beamline X-24A at the National Synchrotron Light Source was designed for optimal performance in the x-ray spectral region 500–5000 eV. This choice of energy range placed a number of constraints on the beamline design, requiring a crystal monochromator in a windowless UHV environment. Although this increased the complexity of the design, there were compelling scientific reasons for our desire to work in this range. In addition to tunability over the selected energy range, a primary goal was to obtain the highest possible energy resolution in the primary beam. We have achieved incident energy resolution significantly better than the typical core-level lifetime broadening for this energy range. This has permitted studies of processes that are not broadened by lifetimes, such as resonant scattering and back-reflection x-ray standing-wave effects. In addition to high resolution, it was designed to collect and focus as much flux as possible from the bending magnet source.
    Type of Medium: Electronic Resource
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