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  • American Institute of Physics (AIP)  (64)
  • 2000-2004  (18)
  • 1995-1999  (46)
  • 1
    Electronic Resource
    Electronic Resource
    A three-dimensional wave-packet method for the CH overtone spectroscopy and intramolecular vibrational relaxation dynamics of the fluoroform molecule (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 445-456 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The overtone spectroscopy and intramolecular vibrational relaxation dynamics of CH chromophore in the fluoroform molecule is studied by a three-dimensional (3D) time-dependent wave-packet method, and the results are compared with the experiment and with those of a 2D (stretch–bend) wave-packet method. A third mode (CF symmetrical stretch) is included in order to explain the long time dynamics and the combination bands between the CF stretch fundamental and the Fermi polyad frequencies. The comparison with the 2D study is carried out by the use of a full set of dynamical and spectroscopic variables, based on the autocorrelation function of the bright states of each polyad. The spectroscopic variables then follow by Fourier transforming the autocorrelation function, while the dynamical ones emerge via survival probability in the frame of the dynamical statistical ensemble. These include several relaxation times and the number of cells and rates of phase–space exploration. The specific effect of the third mode is monitored by following the reduced dynamics of the system irrespective of the polyad stretch–bend dynamics, through population evolution. Dynamical results clearly reveal the third mode effects at very short and long times. In the last regime, we can observe a great span of different behaviors, depending on how the third mode excited states are involved. This richer variety of dynamical patterns cannot be observed in a two-mode model and justifies the present work. The spectroscopic results of both models are in good agreement with the experimental results. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473386
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  • 2
    Electronic Resource
    Electronic Resource
    Geometry of multisymplectic Hamiltonian first-order field theories (2000)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 41 (2000), S. 7402-7444 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: In the jet bundle description of field theories (multisymplectic models, in particular), there are several choices for the multimomentum bundle where the covariant Hamiltonian formalism takes place. As a consequence, several proposals for this formalism can be stated, and, on each one of them, the differentiable structures needed for setting the formalism are obtained in different ways. In this work we make an accurate study of some of these Hamiltonian formalisms, showing their equivalence. In particular, the geometrical structures (canonical or not) needed for the Hamiltonian formalism, are introduced and compared, and the derivation of Hamiltonian field equations from the corresponding variational principle is shown in detail. Furthermore, the Hamiltonian formalism of systems described by Lagrangians is performed, both for the hyper-regular and almost-regular cases. Finally, the role of connections in the construction of Hamiltonian field theories is clarified. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1308075
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  • 3
    Electronic Resource
    Electronic Resource
    The Jacobi–Wilson method: A new approach to the description of polyatomic molecules (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2099-2105 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new method adapted to the calculation of excited rovibrational states of semirigid molecules. It first relies on a description of the molecule in terms of polyspherical coordinates of Jacobi vectors, in order to obtain a compact expression for the kinetic energy operator T(circumflex)(q). This general description is then adapted to the molecule considered by defining curvilinear normal modes from the corresponding zero order harmonic Hamiltonian H(circumflex)0=T(circumflex)(qeq)+Vharm(q), the solutions of which are being used as the working basis set. The residual kinetic term ΔT(circumflex) is treated mainly analytically in this basis, and displays no radial contribution. Anharmonic coupling ΔV(q) is handled by means of a pseudospectral scheme based on Gauss Hermite quadratures. This method is particularly adapted to direct iterative approaches which only require the action of H(circumflex) on a vector, without the need of the associated matrix, thus allowing ultralarge bases to be considered. An application to the excited vibrational states of the HFCO molecule is presented. It is shown in this example that energy levels can be trivially assigned from the leading expansion coefficient of the associated eigenvector. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1337048
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  • 4
    Electronic Resource
    Electronic Resource
    Electro-acoustic damping effects on the parametric decays of electromagnetic waves in electron–positron plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 4916-4922 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Parametric decays of a linearly polarized electromagnetic wave in an electron–positron plasma, including weakly relativistic effects and damping on the electro-acoustic pseudomodes, are studied. The effect of nondissipative Landau damping is simulated through a phenomenological collisional-like term in the fluid equations. It is shown that in general, there are a number of instabilities due to the coupling between electro-acoustic and electromagnetic pseudomodes, and between electromagnetic modes. On the other hand, damping effects reduce the growth rate of these instabilities and increase the instability range. It is also shown that there are no threshold effects on any of the decay modes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1322065
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  • 5
    Electronic Resource
    Electronic Resource
    Optical properties of BeCdSe/ZnCdMgSe strained quantum well structures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5135-5138 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the optical properties of BeCdSe/ZnCdMgSe single quantum well (QW) structures that consist of closely lattice matched ZnCdMgSe barrier layers and a strained BeCdSe QW layer (Δa/a=1.95%) grown on InP substrates. Emission from the red to the green regions of the visible spectrum was obtained from the structures with the QW thickness varying from 95 to 12 Å. Efficient QW emission, dominated by an exciton recombination behavior, was observed. From the Arrhenius plot of the integrated emission intensity as a function of temperature, an activation energy of 61 meV was obtained for a BeCdSe QW structure with a 48 Å thick QW layer. Parameters that describe the temperature dependence of the near band edge emission energy and the broadening of the excitonic emission were evaluated. Our results indicate that the BeCdSe-based QW structures are attractive for application as red light emitters. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413232
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  • 6
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘Parametric decays of a circularly polarized electromagnetic wave in an electron–positron plasma' " [Phys. Plasmas 6, 633 (1999)] (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 635-635 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this response we shall rebut what we consider to be misleading statements in the comment by Shukla and Stenflo (hereafter referred to as SS). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873219
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  • 7
    Electronic Resource
    Electronic Resource
    AlxGa1−xN:Si Schottky barrier photodiodes with fast response and high detectivity (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2146-2148 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gold and nickel Schottky barrier photovoltaic detectors have been fabricated on Si-doped AlxGa1−xN layers (0≤x≤0.22) grown on sapphire by metalorganic vapor phase epitaxy. Responsivity is independent of the Schottky metal or diode size, and also of the incident power in the range measured (10 mW/m2–2 kW/m2). A higher visible rejection has been observed in the spectral response of Au photodiodes (〉103). Time response is resistance-capacitance limited, with time constants as short as 14 ns in Al0.22Ga0.78N diodes. Low frequency noise studies are also presented, and detectivities of 6.1×107 and 1.2×107 mHz1/2 W−1 are determined in GaN/Au and Al0.22Ga0.78N/Au detectors, at −2 V bias. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122405
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  • 8
    Electronic Resource
    Electronic Resource
    Comparison between disaccommodation and ferromagnetic resonance measurements in polycrystalline yttrium–iron–garnet samples : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5436-5438 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline yttrium–iron–garnet (YIG) samples were sintered in air at temperatures ranging from 1350 to 1450 °C. Ferromagnetic resonance measurements have been accomplished at 11 GHz from 77 to 350 K. The different contributions to the linewidth have been analyzed. These results are compared with previous measurements of magnetic disaccommodation in the same samples. A qualitative relationship between both kind of measurements for polycrystalline YIG samples by means of an induced anisotropy formalism is provided. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362331
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  • 9
    Electronic Resource
    Electronic Resource
    The T1(nπ*)←S0 laser induced phosphorescence excitation spectrum of acetaldehyde in a supersonic free jet: Torsion and wagging potentials in the lowest triplet state (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2547-2552 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser induced T1(nπ*)←S0 phosphorescence excitation spectrum of jet-cooled acetaldehyde has been observed for the first time with a rotating slit nozzle excitation system. The vibronic origins were fitted to a set of levels that were obtained from a Hamiltonian that employed flexible torsion-wagging large amplitude coordinates. The potential surface extracted from the fitting procedure yielded barriers to torsion and inversion of 609.68 and 869.02 cm−1, respectively. Minima in the potential hypersurface at θ=61.7° and α=42.2° defined the equilibrium positions for the torsion and wagging coordinates. A comparison to the corresponding S1-state parameters showed that the torsion barrier (in cm−1) does not greatly change, S1/T1=710.8/609.7, whereas the barrier height for the wagging-inversion barrier increases dramatically, 574.4/869.0. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472120
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  • 10
    Electronic Resource
    Electronic Resource
    Study of the optical properties of fused quartz after a sequential implantation with Si and Au ions (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1574-1576 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Implantation of Au ions into Si-implanted fused quartz strongly enhances the photoluminescence (PL) intensity around 630 nm measured after subsequent sample annealing at 900 °C. This effect is attributed to the enhancement of the formation of Si nanocrystals by the presence of Au ions and not by ion-implantation-induced defects. This conclusion was deduced by monitoring the defect formation in fused silica by 2 MeV Si ion implantation with doses ranging from 2×1016 to 1×1017 Si/cm2. Some of the 4×1016 Si/cm2-implanted samples were reimplanted at a similar depth with 10 MeV Au ions at doses of 4×1016 and 1.2×1017 Au/cm2. The absorption spectroscopy, electron paramagnetic resonance and PL measurements show the presence of B2 and E′ matrix point defects in as-prepared Si-implanted samples. As these defects disappear after annealing at 600 °C, the presence of a strong PL peak in samples implanted and annealed at 900 °C strongly suggests that the observed luminescence is produced by Si nanoparticle formation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122208
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