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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper reports three independent studies. In the first study, the infrared band shapes and relative intensities of gaseous thiirane-d4 (ethylene sulfide-d4, C2D4S), the Raman spectrum of liquid thiirane-d4, and infrared spectra of gaseous cis- and trans-1, 2-dideuteriothiirane, (CHD)2S, are reported for the first time. The vibrational spectra of C2H4S, C2D4S, and some bands of cis-(CHD)2S are assigned from the symmetry analysis, group frequencies, infrared band shapes, and Raman polarization data. The frequencies so assigned are used to derive a modified valence force field, (MVFF), which reproduces them well, allows the remaining fundamental frequencies of cis-(CHD)2S to be found, and allows the spectrum of trans-(CHD)2S to be assigned. The MVFF is then further refined to optimize the fit to the 46 assigned frequencies of the four molecules. Twenty four nonzero force constants fit the 46 frequencies with an average error of 0.4%. The assignment is thus well based and self-consistent. Inthe second study, ab initio SCF calculations of optimum geometry, vibrational frequencies, and IR intensities of thiirane, thiirene, and a number of isotopically substituted derivatives are reported for the 6-31G*, 3-21G, and STO 3G bases. The force constants of thiirane from the 6-31G* basis are in good agreement with those of the MVFF when allowance is made for the fact that some were constrained to zero in the MVFF. The potential energy distributions from the ab initio and normal coordinate calculations agree well, with the former confirming some defects in the latter. The 6-31G* force constants multiplied by 0.80 reproduced the 46 observed frequencies with an average error of 1.4%. For thiirene and isotopic derivatives, the 6-31G* IR spectra are in much better agreement with experiment than previous results with smaller bases. In particular, significantly higher frequency C–S stretches are predicted with the 6-31G* basis. Nevertheless, a few discrepancies remain between experiment and the 6-31G* SCF results. In the third study, vibrational frequencies and IR intensities of thiirene and isotopic derivatives were evaluated at the CISD level of theory using a standard DZP basis set. In the DZP-CISD thiirene spectrum, the B1 C–H out-of-plane bend and its position relative to the A1 C–S stretch differ significantly from the 6-31G* SCF results, giving confirmation of the experimental assignments. However, the same DZP-CISD force constants predict that two low-frequency bands of thiirene-d1 are assigned incorrectly. No other significant discrepancies between theory and experiment remain for the thiirene species.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 2691-2697 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The key features of the H+O3 potential energy surface have been determined using ab initio quantum mechanical methods. The electronic wave function used is a multiconfiguration Hartree–Fock wave function which provides a qualitatively correct description of various reactive channels. It is found that the H+O3→HO+O2 reaction proceeds along a nonplanar pathway in which the H atom descends vertically to the plane containing the ozone molecule to form an HO3 intermediate which then undergoes fragmentation. No planar transition state for a direct O-atom abstraction could be located. The radical–radical O+HO2 reaction was found to have no energy barrier to formation of HO3 which was determined to subsequently decompose to HO+O2. The H-atom abstraction reaction O+HO2→OH+O2 was found to have a small activation energy. The dynamical implications of these findings are discussed. The results are consistent with the observed vibrational excitation of the OH product in the H+O3 reaction. The key features of the H+O3 potential energy surface are expected to be transferable to the X+O3 systems where X=Cl, OH, NO, and NH2.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to study the formation of thermal vacancies in the Ti–Al alloy system, high-temperature positron lifetime measurements together with a modeling of defect formation in the framework of nearest-neighbor pair bonds were performed for α2Ti3Al and compared to recent results on γTiAl [U. Brossmann, R. Würschum, K. Badura, and H.-E. Schaefer, Phys. Rev. B 49, 6457 (1994)]. Substantial increases of the positron lifetime τ were observed for Ti65.6Al34.4 and Ti77.1Al22.9 in the temperature range T(approximately-greater-than)1200 K where thermal vacancy concentrations above the detection limit of positron annihilation are expected from the model calculations for the α2 phase. Within the high-temperature increase of the positron lifetime in the α2 and the β phase single-component positron lifetime spectra were observed. This behavior is in contrast to the two-component spectra observed conventionally at intermediate positron trapping rates and is attributed to a fast detrapping and retrapping of positrons at vacancies due to a low positron–vacancy binding energy. For this case, a vacancy formation enthalpy of HFV=(1.55±0.2) eV in α2Ti65.6Al34.4 and HFV=(1.8±0.2) eV in βTi77.1Al22.9 can be derived. These results are discussed in the context of recent 44Ti tracer diffusion studies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the first time clear evidence for two-dimensional Shubnikov–de Haas oscillations in modulation-doped CdTe/CdMnTe quantum-well structures is reported. The structures were grown by molecular-beam epitaxy using ZnBr2 as a novel source material for the n-type doping of II-VI epitaxial layers. From an analysis of the Shubnikov–de Haas oscillations a carrier density of 9×1011 cm−2 and an effective mass of 0.1 m0 could be deduced. Due to band filling the Fermi energy in the subbands is shifted above the conduction-band edge. This can be detected as a Stokes shift of absorption compared to photoluminescence recombination. From the Fermi energy shift the carrier concentration can be estimated, which agrees well with values determined by Hall-effect measurements.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2271-2273 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial iron disilicide thin layers have been grown on silicon by gas source molecular beam epitaxy (GSMBE) in the temperature range 450–550 °C. Fe(CO)5 and SiH4 are used as sources for the silicide growth on a heated Si(111) surface. The growth phases are characterized in situ by means of high-resolution electron energy loss spectroscopy, ultraviolet and x-ray photoelectron spectroscopies. The formation of an epitaxial metallic γ-FeSi2 layer at the interface with the silicon substrate is revealed and no complete relaxation of this strained metastable interface layer is observed, as the growth proceeds with the semiconducting equilibrium β-FeSi2 phase. The coexistence in the GSMBE grown heterostructures of the metallic (CaF2) and semiconducting (orthorhombic) FeSi2 structures is confirmed by cross-section transmission electron microscopy.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to study the influence of the nanocrystalline microstructure on the magnetic properties of pure nanocrystalline metals, in situ magnetic measurements of high-purity nanocrystalline nickel, prepared by a gas-condensation technique with subsequent compaction at various pressures have been performed. The approach to ferromagnetic saturation indicates free volumes in the nanocrystalline system of the size of individual missing crystallites as well as internal stresses. While the saturation polarization of the nanocrystalline Ni samples appears to be unchanged compared to coarse-grained Ni the coercive field and magnetic domains are strongly influenced by the nanocrystalline structure. The shape of the domains with sizes of 10–200 μm much larger than the crystallite size depends on the annealing state of the specimen. The initial coercive field increases with the compaction pressure during preparation. Upon annealing it further increases to a maximum value at Ta=500 °C and decreases at higher annealing temperatures. Additionally, the effect of oxygen located in the grain boundaries has been studied. © 1996 American Institute of Physics.
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  • 7
    Publication Date: 2016-01-06
    Description: The performance and degree of efficiency of industrial transformers are directly influenced by the magnetic properties of high-permeability steel laminations (HPSLs). Industrial transformer cores are built of stacks of single HPSLs. While the insulating coating on each HPSL reduces eddy-current losses in the transformer core, the coating also induces favorable inter-granular tensile stresses that significantly influence the underlying magnetic domain structure. Here, we show that the neutron dark-field image can be used to analyze the influence of the coating on the volume and supplementary surface magnetic domain structures. To visualize the stress effect of the coating on the bulk domain formation, we used an uncoated HPSL and stepwise increased the applied external tensile stress up to 20 MPa. We imaged the domain configuration of the intermediate stress states and were able to reproduce the original domain structure of the coated state. Furthermore, we were able to visualize how the applied stresses lead to a refinement of the volume domain structure and the suppression and reoccurrence of supplementary domains.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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