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  • 1
    Electronic Resource
    Electronic Resource
    A photoion–photoelectron coincidence study of (CO)2 (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4098-4099 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoion–photoelectron coincidence (PIPECO) spectrum for (CO)+2 has been measured in the wavelength region of ∼600–1 000 A(ring). The lower limits for the bond dissociation energies of CO+ (X˜)⋅CO, CO+ (A˜)⋅CO, and CO+ (B˜)⋅CO are determined to be 29.8, 17, and 16 kcal/mol, respectively. Evidence supporting the existence of long-lived (CO)+2 states with dissociation lifetimes 〉40 μs at energies above the CO+ (X˜,v=0)+CO asymptote is found. The dissociative lifetimes of CO+ (A˜)⋅CO and CO+(B˜)⋅CO are estimated to be longer than 4 μs and 50 ns, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453814
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  • 2
    Electronic Resource
    Electronic Resource
    A photoion–photoelectron coincidence study of Arn (n=2–4) (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2995-3003 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoion–photoelectron coincidence (PIPECO) spectra for Ar+n (n=2–4) in the wavelength region of 750–875 A(ring) have been measured at different nozzle stagnation pressures. The ionization energies (IE) for the ground Ar+2[I(1/2)u] and Ar+3[I(1/2)u] states are determined to be 14.518±0.017 eV (854±1 A(ring)) and 14.350±0.033 eV (864±2 A(ring)), in agreement with the findings of previous photoionization experiments. The IE for Ar+2[II(1/2)u] is found to be (approximately-less-than)15.83 eV (783 A(ring)). The observation of the Ar+2[II(1/2)u] PIPECO band supports the interpretation that Ar+2[II(1/2)u] is metastable with a lifetime longer than 47 μs, a value in accord with the calculated radiative lifetime of 90.9 μs for the II(1/2)u →I(1/2)g transition. The PIPECO spectrum for Ar+2 is dominated by autoionization structure similar to that resolved in the photoionization efficiency spectrum for Ar+2, indicating that a significant fraction of electrons produced by these autoionizing states are slow electrons with near-zero kinetic energies. Evidence is found that metastable Ar+3 and Ar+4 ions formed by photoionization of Ar3 and Ar4 at energies above the Ar+2[I(1/2)u]+Ar(1S0) and Ar+3[I(1/2)u]+Ar(1S0) dissociation limits may live longer than 58 and 66 μs, respectively. We suggest that the formation of Ar+3 in metastable electronic states may be responsible for the long dissociation lifetimes of Ar+3 observed in this experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455901
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  • 3
    Electronic Resource
    Electronic Resource
    A photoion–photoelectron coincidence study of (CO)2 and (CO)3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6026-6033 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoion–photoelectron coincidence (PIPECO) spectra for (CO)+2 in the wavelength region of 620–990 A(ring) have been obtained at different nozzle stagnation pressures (P0). The ionization energy for (CO)2 to CO+(X˜)⋅CO is determined to be (approximately-less-than)12.73±0.05 eV (974±4 A(ring)), indicating that CO+(X˜)⋅CO is bound by more than 1.29 eV. The PIPECO measurements also provide evidence that CO+(A˜,B˜)⋅CO are bound with dissociation energies 〉0.3 eV. At P0≤200 Torr and a nozzle temperature (T) of 120 K, nozzle expansion conditions which minimize the formation of (CO)n (n≥3), the intensities for the CO+(A˜,B˜)⋅CO PIPECO bands are found to be negligibly small compared to that for the CO+(X˜)⋅CO PIPECO band. This observation supports the conclusion that the excited CO+(A˜,B˜)⋅CO ions are dissociative, with dissociation lifetimes〈42 μs. This conclusion is contrary to that of the preliminary study which is based on the PIPECO spectrum for (CO)+2 measured at P0=350 Torr and T=120 K. Assuming that the radiative lifetimes of CO+(A˜ or B˜) and CO+(A˜ or B˜)⋅CO are identical, we estimate that the dissociation lifetimes for CO+(A˜)⋅CO and CO+(B˜)⋅CO are (approximately-less-than)4 μs and (approximately-less-than)50 ns, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456368
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  • 4
    Electronic Resource
    Electronic Resource
    The electronic structure of polyaniline and doped phases studied by soft x-ray absorption and emission spectroscopies (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 4756-4761 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant soft x-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped (protonated) phases for both the carbon and nitrogen contents. The resonant x-ray emission spectra show depletion of the π electron bands due to the selective excitation which enhances the effect of symmetry selection rules. The valence band structures in the x-ray emission spectra attributed to the π bands show unambiguous changes of the electronic structure upon protonation. By comparing to x-ray absorption measurements, the chemical bonding and electronic configuration is characterized. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479238
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  • 5
    Electronic Resource
    Electronic Resource
    Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5990-5996 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer π band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476011
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  • 6
    Electronic Resource
    Electronic Resource
    Properties and chemical stability of hot-rolled Ag(7 at. % Cu)-sheathed Bi2Sr2Ca0.64Cu1.64Ox powder-in-tube tapes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4596-4607 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bi2Sr2Ca0.64Cu1.64Ox (nominally Bi2212) powders were fabricated into powder-in-tube Ag- and Ag(7 at. % Cu)-sheathed tapes by cold and hot rolling to investigate the effects of sheath composition and rolling conditions on their microstructural development and superconducting properties. Bi2212 tapes with Ag(Cu) sheaths exhibited improved grain alignment and interfacial uniformity, as well as enhanced formation of the Bi-free phase (≈Sr7.5Ca6.5Cu14Ox), relative to the Ag-sheathed specimens. The hot-rolled Ag(Cu)-sheathed tapes displayed superior critical current densities (Jc), where magnetization Jcm=1.5×106 (H(parallel)c) and 4.6×105 A/cm2 (H⊥c) at T=5 K, H=1 T. Correspondingly, these specimens had transport critical current densities (Jct) of 6.7×104 A/cm2 (H(parallel)c) and 5.4×104 A/cm2 (H⊥c) at T=4.2 K, H=0 T and 2.2×104 A/cm2 (H(parallel)c) and 3.0×104 A/cm2 (H⊥c) at T=4.2 K, H=14 T. The chemical stability of the Ag(Cu) sheath regions during the partial melting process was also studied. Rapid oxidation of copper produced Cu2O precipitates in the sheath at 885 °C, and subsequently a Cu2O-free zone developed near the core/sheath interface. A theoretical analysis of Cu2O precipitate formation and decomposition during thermal processing is presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359805
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  • 7
    Electronic Resource
    Electronic Resource
    Electromagnetic modes and prism-film coupling in anisotropic planar waveguides of epitaxial (101) rutile thin films (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7823-7830 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report optical waveguiding in single-crystal, epitaxial (101) oriented rutile (TiO2) thin films grown on (112¯0) sapphire (α-Al2O3) substrates using the metal-organic chemical vapor deposition technique. The electromagnetic field distributions and propagation constants for asymmetric planar waveguides composed of an anisotropic dielectric media applicable to these films are derived. Modifications to the prism-film coupling theory for this anisotropic case are also discussed. By application of this model to (101) oriented rutile thin films, we directly obtain values of the ordinary and extraordinary refractive indexes, n0 and ne, of the rutile thin films as well as film thicknesses. We obtain typical values of the refractive indexes (n0=2.5701±0.0005; ne=2.934±0.001) near to those for bulk rutile single crystals indicating the exceptional quality of these films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353931
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  • 8
    Electronic Resource
    Electronic Resource
    First results from the SpectroMicroscopy Beamline at the Advanced Light Source : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1342-1345 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The SpectroMicroscopy Facility at the Advanced Light Source is based on a high brightness, high-resolution beamline, and includes a collection of projects designed to exploit the unique characteristics of the soft x-ray beam. The beamline itself is comprised of a 5-m long, 5-cm-period undulator, a spherical-grating monochromator with water-cooled gratings. Adaptive optics refocus the monochromatic beam to two "microfocus'' experimental stations with spot sizes less than 50 μm diameter and a third "nanofocus'' station uses a zone-plate lens to further demagnify the microfocus spot. Experimental stations include an "ultraESCA'' spectrometer for small-area spectroscopy and photoelectron diffraction, a scanning transmission x-ray microscope, and photoelectron microscopes. Commissioning experiments of microscopic actinide photoemission, surface-core-level photoelectron diffraction, and high-resolution soft x-ray fluorescence demonstrate dramatic improvements in sensitivity due to the high brightness and small focus of the beamline. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145969
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  • 9
    Electronic Resource
    Electronic Resource
    End station for polarization and excitation energy selective soft x-ray fluorescence spectroscopy : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1561-1563 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An end station for soft x-ray fluorescence spectroscopy has been constructed, which includes an experiment chamber, rotatable 90° under ultrahigh vacuum conditions around the incoming synchrotron radiation beam, which is provided with a high-resolution soft x-ray spectrometer. A manipulator allowing three axes of rotation, three directions of translation, as well as LN2 cooling and resistive heating is mounted to the chamber and serves as the sample holder. Samples can be transferred under vacuum between the experiment chamber and two other chambers, one for sample preparation and another for introducing new samples and for sample storage. The end station has been used at two different synchrotron radiation laboratories (beamline BW3) at HASYLAB in Hamburg and at ALS (beamline 7.0) in Berkeley. Polarization-dependent and angular resolved, selectively excited x-ray emission studies have been made on ordered as well as nonordered systems, e.g., high-Tc superconducting systems, diamond, fullerenes, and molecular ices. The experimental system will be presented along with some recent scientific results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145908
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  • 10
    Electronic Resource
    Electronic Resource
    Adjustable boron carbonitride nanotubes (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5325-5333 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The adjustable photoluminescence (PL) and field electron emission (FEE) properties of boron carbonitride (B–C–N) nanotubes grown under well-controlled conditions are studied systematically. Large-scale highly aligned B–C–N nanotubes are synthesized directly on Ni substrates by the bias-assisted hot filament chemical vapor deposition method. Single-walled B–C–N nanotubes and nanometric B–C–N heterojunctions are obtained by the pulsed-arc-discharge technique and pause-reactivation two-stage process, respectively. It is found that the microstructures, orientations, and chemical compositions of the nanotubes can be controlled by varying growth parameters. The mechanism of the controllable growth is also investigated. Intense and stable PL from the nanotubes is observed in both blue-violet (photon energies 3.14–2.55 eV) and yellow-green bands (photon energies 2.13–2.34 eV) and the emission bands are adjusted by varying the compositions of the nanotubes. FEE properties are also studied and optimized by varying the B or N atomic concentrations in the nanotubes. All these results verify the controllability of the electronic band structure of the B–C–N nanotubes. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459596
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