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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2048-2050 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We tested the theoretical prediction that the band structures on the opposite sides of a homojunction can be artificially displaced in energy with respect to each other by means of double intralayers of atomiclike thickness, producing band discontinuities of potential interest for practical applications. Evidence of such discontinuities was found when Ga-As, Al-As, Ga-P, or Al-P intralayers were inserted between Si and Si or Ge and Ge.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5363-5376 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Four isotopes of the methanol cation radical (CH3OH+) have been generated by three independent methods and isolated in neon matrices at 4 K for a detailed electron spin resonance (ESR) investigation. The ion generation methods employed were X irradiation, photoionization, and electron ionization. The nuclear hyperfine (A tensors) measurements were compared with those obtained from ab initio extended basis set multireference configuration interaction (CI) wave functions. The relationships between geometry and electronic structures were fully explored. The trend in the large isotropic methyl hydrogen A values for the isoelectronic series CH3F+, CH3OH+, and CH3NH2+ was found to follow the trend in dissociation energies for these radical cations. The neon magnetic parameters for CH3OH+ are gx=2.0036(4) and gz=2.010(1); Aiso (methyl hydrogens)=229(1) MHz, ||Ax||=54(2) and ||Az||=80(3) MHz for the hydroxy hydrogen; ||Ax||=40(2) and ||Az||=29(4) MHz for 13C. The observed magnetic parameters for CH2DOH+ indicate an unusually large deuterium effect Aiso (CH2)=329 MHz with ||Aiso||=4.1(3) MHz for the methyl deuterium. These results show that averaging of the methyl hydrogen environments is occurring on the ESR time scale.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2987-2995 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The new diatomic radicals PdB and PdAl have been generated by depositing the products produced from the pulsed laser vaporization of the elemental mixtures into neon matrices at 4 K. ESR (electron spin resonance) studies of these matrix isolated radicals, including an analysis of the 105Pd(I=5/2), 27Al(I=5/2), and 11B(I=3/2) nuclear hyperfine interactions, show that both have X 2Σ electronic ground states. These new results are compared with previous ESR measurements for PdH, PdCH3, YPd, ScPd, and PdH2+ to reveal electronic structure information and bonding trends as the complexity of the ligand increases 1s, 2p, 3p, 3d, and 4d. Ab initio UHF (unrestricted Hartree–Fock) theoretical calculations were also conducted on four of these small palladium radicals as part of this experimental investigation. A simple interpretation of the 105Pd hyperfine interactions and molecular g tensors based on the degree of charge transfer to palladium is presented. The observed magnetic parameters (MHz) for 105Pd11B in a neon matrix at 4 K are g(parallel)=2.009(2), g⊥=2.042(2), A(parallel)=−1483(15), and A⊥=−1483(2) for 105Pd, and A(parallel)=197(4) and A⊥=140(1) for 11B. The parameters for 105Pd27Al are g(parallel)=2.010(1), g⊥=2.0343(5), A(parallel)=−1283(10) and A⊥=−1268(2) for 105Pd, and A(parallel)=182(2) and A⊥=84.6(5) for 27Al.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The first spectroscopic investigation of 89Y 10B+, 89Y 11B+, and 89Y 27Al+ is reported, revealing that both of these diatomic cation radicals have X 4Σ− electronic ground states. The ions were generated by three high energy techniques in combination with neon matrix isolation at 4 K and studied by electron spin resonance (ESR) spectroscopy. The generation methods included pulsed laser vaporization of the metal alloys, photoionization at 16.8 eV during matrix deposition, and x-irradiation at 80 keV of the matrix sample following deposition. Hyperfine interactions were resolved for all of the above nuclei and were compared with calculated isotropic and dipolar components of the A tensor. The yttrium 5s character observed in YAl+ was significantly larger than that in YB+ based upon the observed nuclear hyperfine interactions. The calculated electronic structure properties showed agreement with this trend in the observed Aiso parameters. In addition, qualitative descriptions of the bonding properties are also presented which are consistent with the magnetic parameters obtained from the ESR measurements. The magnetic parameters for Y 11B+ in neon at 4 K are g⊥=1.959(1), A⊥ (Y)=33.6(4) MHz, and A⊥(11B)=65.9(4) MHz. For YAl+, g⊥=1.942(1), A⊥=142(1) MHz, and A⊥(Al)=73(1) MHz.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The first experimental spectroscopic study of the SiB and SiAl diatomic radicals is reported. Electron spin resonance results indicate that both molecules have X 4Σ ground electronic states, in agreement with earlier theoretical calculations. The SiB and SiAl radicals were generated in neon matrices at 4 K by trapping the products produced from the pulsed laser vaporization of their alloys. Electronic structure information for these radicals is especially interesting given the utilization of silicon doped materials in semiconductor applications. The observed nuclear hyperfine interactions (A tensors) for 10B, 11B, and 27Al in these molecular radicals were compared with the results of ab initio configuration-interaction theoretical calculations which were conducted as part of this experimental study. The neon matrix magnetic parameters (MHz) for Si 11B are D=800(2), g(parallel)=2.0014(8), g⊥=2.0005(4), A⊥=92.4(5), and A(parallel)=111(2). For Si 27Al the results (MHz) are D=9710(2), g(parallel)=1.9994(8), and g⊥=1.9978(4), ||A⊥||=10.3(6), and ||A(parallel)||=43.5(8).
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 1058-1070 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Experimental observations of a purely elastic flow instability occurring in the lid-driven cavity flow of two semi-dilute polymer solutions are reported and the effect of cavity aspect ratio on the dynamical structure of the unstable flow is quantitatively investigated. The spatial and temporal characteristics of the secondary flow are measured using flow visualization, laser Doppler velocimetry, and digital particle image velocimetry. At the onset conditions the disturbances appear in the form of spatially periodic flow cells which propagate along the neutral direction of the cavity. The secondary flow structure is analogous to the Taylor–Görtler vortices observed in inertially driven hydrodynamic instabilities. The critical onset conditions for two elastic test fluids and five different aspect ratios correlate with a recently proposed dimensionless stability criterion which incorporates measures of the local streamline radius of curvature and the non-Newtonian normal stresses in the flow domain. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 30-47 
    ISSN: 1089-7666
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using the lubrication approximation we investigate the spreading of a finite-sized thin drop of incompressible Newtonian fluid on a planar substrate subjected to a jet of air blowing normally to the substrate. Three specific problems are studied in detail: a jet of air acting normally to the substrate when gravity effects are negligible, a jet of air directed vertically downward onto a sessile drop on a horizontal substrate, and a jet of air directed vertically upward onto a pendent drop on a horizontal substrate. The dynamics of the moving contact line are modeled by means of a generalized "Tanner Law" relating the contact angle to the speed of the contact line. Both symmetric two-dimensional and axisymmetric three-dimensional geometries are considered; the latter case is equivalent to that of an axisymmetric drop spreading on a substrate rotating with constant angular velocity (the simplest model for spin coating). Quasistatic solutions for the drop profile are obtained in the limit of small capillary number and the stability of equilibrium solutions to small perturbations is determined. The analysis is then extended to include drops with a dry patch at their center which are found to be unconditionally unstable in all the cases investigated. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7384-7392 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Detailed experimental and theoretical electron spin resonance (ESR) studies of the cation radicals, PH+3 and P2H+6, isolated in neon and argon matrices are reported. These cations were generated by photoionization (17 eV) and x-irradiation (80 keV) methods. The observed nuclear hyperfine interactions (A tensors) showed reasonable agreement with Aiso and Adipolar values calculated at the ab initio configuration interaction (CI) level. These ESR results for PH+3 clearly indicate its nonplanarity; for P2H+6, an earlier theoretical prediction of a C2h distortion from C3v was confirmed by these new experimental results which reveal two different H atom environments. The neon magnetic parameters for PH+3 are g(parallel)=2.002(1), g⊥=2.007(1), A⊥=920(3), and A(parallel)=1638(15) MHz for 31P and A(H)≤6 MHz. The neon parameters for P2H+6 are g(parallel)=2.001(1), g⊥=2.003(1), A⊥=1527(2), and A(parallel)=1909(4) MHz for 31P and A(2H)=182(2) and A(4H)=±22(2) MHz.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The discandium radical cation, Sc+2, has been isolated in neon matrices at 4 K and studied by electron spin resonance (ESR) spectroscopy and theoretical methods. It was produced by the x-irradiation of neon matrix samples containing neutral Sc2 which was formed by trapping the products generated from the pulsed laser vaporization of scandium metal. The experimental and theoretical findings indicate that Sc+2 has a 4Σ−g electronic ground state compared to an X 5Σ−u state for the neutral discandium radical. The large decrease in the 45Sc hyperfine interaction (A tensor) going from Sc2 to Sc+2 provides direct experimental information concerning the types of valence molecular orbitals that are involved in these diatomic radicals. The neon matrix magnetic parameters for 45Sc+2 are g(parallel)≈2.00, g⊥=1.960(1), ||A(parallel)||=28(6), and ||A⊥||=26.1(3) MHz; the D value (zero field splitting) was 15 381(3) MHz. Ab initio configuration interaction (CI) calculations of the nuclear hyperfine interactions yielded results in reasonable agreement with the experimental observations.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1332-1332 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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