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  • 1
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 25 (1986), S. 276-284 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4344-4347 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ultraviolet absorption cross sections of ν3 vibration-excited UF6 molecules were measured in the wavelength region between 230 and 280 nm. The state-selective excitation was accomplished by 16 μm laser pumping of the ground vibrational state of flow-cooled UF6. Maximum changes in the absorption cross sections were observed toward longer wavelengths in the wings of the two charge transfer bands located at 220 and 260 nm. The results are discussed in terms of a transition from the ν3 vibrationally excited state to an upper dissociative potential surface. The change in the UV absorption cross section was also monitored as a function of the IR laser frequency and the sample gas temperature. The IR excitation spectrum follows qualitatively the low resolution contour of the ν3 Q branch. The magnitude in the absorption change is dependent on the fraction of molecules being accessed by the IR laser. The characteristic relaxation time for the ν3 excitation was estimated to be about 0.25 μs Torr at 100 K.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4042-4047 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute cross sections are measured for electron impact ionization and dissociative ionization of SiF2 from threshold to 200 eV. A fast (3 keV) neutral beam of SiF2 is formed by charge transfer neutralization of SiF+2 with Xe; it is primarily in the ground electronic state with about 10% in the metastable first excited electronic state (a˜ 3B1). The absolute cross section for ionization of the ground state by 70 eV electrons to the parent SiF+2 is 1.38±0.18 A(ring)2. Formation of SiF+ is the major process with a cross section at 70 eV of 2.32±0.30 A(ring)2. The cross section at 70 eV for formation of the Si fragment ion is 0.48±0.08 A(ring)2. Ion pair production contributes a significant fraction of the positively charged fragment ions.
    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 89 (1988), S. 4035-4041 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absolute cross sections for electron-impact ionization of the SiF3 free radical from threshold to 200 eV are presented for formation of the parent SiF+3 ion and the fragment SiF+2, SiF+, and Si+ ions. A 3 keV beam of SiF3 is prepared by near-resonant charge transfer of SiF+3 with 1,3,5-trimethylbenzene. The beam contains only ground electronic state neutral radicals, but with as much as 1.5 eV of vibrational energy. The absolute cross section for formation of the parent ion at 70 eV is 0.67±0.09 A(ring)2. At 70 eV the formation of SiF+2 is the major process, having a cross section 2.51±0.02 times larger than that of the parent ion, while the SiF+ fragment has a cross section 1.47±0.08 times larger than the parent. Threshold measurements show that ion pair dissociation processes make a significant contribution to the formation of positively charged fragment ions.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1511-1518 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements of millimeter and submillimeter wavelength emission (240 GHz〈ω/2π〈470 GHz) from a free-electron laser are reported. The laser operates as a superradiant amplifier and without an axial guide magnetic field; focusing and transport of the electron beam through the wiggler interaction region are achieved by means of the bifilar helical wiggler field itself. Approximately 18 MW of rf power has been observed at a frequency of 470 GHz, corresponding to an electronic efficiency of 0.8%. Frequency spectra are measured with a grating spectrometer and show linewidths Δω/ω∼2%–4%. The experimental results are in very good agreement with nonlinear numerical simulations.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 3106-3112 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A stability analysis for the cyclotron-maser instability in the presence of a nongyrotropic electron distribution is presented. The model configuration describes a uniformly magnetized cold ambient plasma that contains a relatively diffuse suprathermal electron component coherently bunched in gyrophase. The stability of perturbations propagating parallel to the ambient magnetic field is considered, and substantial growth rates are found to occur. The results are contrasted with those found for a comparable gyrotropic loss-cone distribution, and it is found that the nongyrotropic instability is characterized by substantially higher growth rates.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 387-393 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear evolution of the free-electron laser amplifier is investigated numerically in the collective Raman regime for a configuration in which a relativistic electron beam propagates through a loss-free cylindrical waveguide in the presence of a helical wiggler and an axial guide magnetic field. A set of coupled nonlinear differential equations is derived that governs the evolution of the TE waveguide modes, the beam space-charge mode, and the trajectories of an ensemble of electrons. Comparison with experiment shows good agreement for cases in which the intersection between the vacuum waveguide mode and the beam resonance line are near "grazing'' (i.e., when the intersections are sufficiently close together to result in one broad gain bandwidth). For interactions in which two distinct gain bands occur, the numerical procedure tends to underestimate the beam–plasma frequency and results in a 15%–20% discrepancy with experiment.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 3179-3181 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both the free-electron laser (FEL) and cyclotron-maser (CM) instabilities can play a role in wave generation laser experiments employing both an axial guide magnetic field and a transverse wiggler magnetic field. The experimental distinction between these two mechanisms can only be made by comparing measured radiation characteristics with the predictions of either model. For a recent intense beam experiment [Phys. Fluids 26, 2683 (1983)], most of the data are in good agreement with the FEL mechanism, as previously concluded, rather than with the CM instability, and the data taken far from gyroresonance are of unambiguous FEL origin.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2579-2585 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Simple graphic methods for illustrating the transformation of x-ray beams by optical elements such as mirrors, monochromators, and slits are very helpful tools when optimizing synchrotron radiation experiments. They provide guidelines for matching the optical components to the source and to the experiment, and for checking the physical meaning of the more detailed results obtained by subsequent ray-tracing calculations. Phase-space diagrams have been used extensively to describe synchrotron radiation experiments by plotting an angular variable against a positional one with the possibility to add the energy in a third dimension. For neutron scattering, the traditional method consists in parallel representations, in reciprocal and in real space, that can also be considered as another kind of phase-space diagram. In this paper, we show the specific advantages and the complementary character of the above diagrams. The representation of several optical elements and their effect on beam transformation is given first individually and then for some arrangements of two or more beam-defining devices. Finally, a beamline is described and optimized as a demonstration of the usefulness and the limits of these graphic methods.
    Type of Medium: Electronic Resource
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