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  • American Institute of Physics (AIP)  (11)
  • Cambridge University Press  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Theoretical prediction of ultrahigh vibrational excitation using infrared picosecond pulse trains: Coherent absorption of several photons each of a different frequency (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3451-3467 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using an IR picosecond pulse train, ultrahigh vibrational excitation in a Morse oscillator is achieved. Following a suggestion by Paramonov and Savva, pulse-train parameters can be chosen such that within 100 pulses (about 20 ps) there is significant excitation into the eighth excited vibrational state. We improve on their work by (1) using physically realistic matrix elements and potential parameters; (2) using Floquet theory to more efficiently perform the numerical calculation; (3) discussing the molecular excitation sensitivity to pulse-train parameters: pulse spacing, pulse width, central laser frequency, and peak laser fluence; and (4) showing that the vibrational excitation is a coherent multicolor, multiphoton process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459767
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  • 2
    Electronic Resource
    Electronic Resource
    Semiclassical quantization of vibrational systems using fast-Fourier transform methods: Application to HDO stretches (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6036-6046 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Based on work by Martens and Ezra and partially developed independently by Eaker, we apply an improved method of approximating the quantum energy levels of a system of coupled oscillators using the fast-Fourier transform of classical coordinates and momenta to find quantizing trajectories. Application is made to a two-dimensional system modeling the stretching motions of the HDO molecule. The results are in excellent agreement with quantum calculations. This method is useful because: (1) it gives results which are independent of any separability of the Hamiltonian, (2) it is not limited in the number of degrees of freedom that can be handled, and (3) no zero-order approximation to the system is necessary. Results are equally valid inside and outside of resonance zones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460441
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  • 3
    Electronic Resource
    Electronic Resource
    Identification of intramolecular energy transfer pathways in a reactive triatomic system (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2948-2957 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model of the HNC/HCN isomerization reaction with three vibrational degrees of freedom is studied. The semiclassical technique of adiabatic switching is used to obtain quantizing trajectories in the metastable HNC potential well. Adjustment of these eigenvalues to account for the degenerate bend mode not included in our model gives agreement to within 20 cm−1 of the quantum results. Isomerization data show that this system has a high degree of mode specificity. Fourier transform analysis of the vibrational motion identifies two pathways for energy transfer. One pathway occurs at high bending quantum numbers and is believed to involve potential features and chaotic motion at high bending angle. The second pathway is a classical resonance in which the sum of the CN stretching frequency and twice the bending frequency is equal to the H atom stretching frequency. The resonance acts to transfer energy into the bending mode which allows the trajectory to reach the high bending angle region of the potential where the first mechanism can cause isomerization. It is determined that the role of the CN mode is to allow for enhanced stretch–bend coupling through a three mode resonance. This study concludes that bending degrees of freedom play a major role in intramolecular energy transfer dynamics in agreement with the results of previous studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455710
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  • 4
    Electronic Resource
    Electronic Resource
    Pyroelectric conversion cycle of vinylidene fluoride-trifluoroethylene copolymer (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 5036-5042 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Copolymers of vinylidene fluoride–trifluoroethylene P(VDF-TrFE) exhibit large piezoelectric and pyroelectric effects. In addition to the most common application of the pyroelectric effect (radiant detection) it is possible to convert heat directly into electrical energy by pyroelectric conversion. This study reports the first pyroelectric conversion cycle to be measured for the copolymer P(VDF-TrFE). It is found that standard isothermal D-E hysteresis loop measurements are not necessarily accurate predictors of pyroelectric conversion performance for this material. Conduction effects are found to obscure the observation of conversion cycles in most cases for the presently available materials. In spite of these difficulties, a conversion cycle was measured whose output electric energy density was 30 mJ/cm3. The output density is 15 times larger than any other polymer previously measured .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335280
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  • 5
    Electronic Resource
    Electronic Resource
    Pyroelectric conversion cycles (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 4709-4716 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the type of power cycle upon the amount of output electrical work for a pyroelectric converter has been measured. Output electrical energy densities are reported for ceramic lead zirconate modified with Sn4+ and Ti4+ in the execution of a variety of thermal-electrical cycles. The effect upon the energy density due to changes in the voltage cycle limits and changes in the load resistance were also studied. A conversion cycle which is an electric analog of the Ericsson cycle is shown to yield the largest output energy density (100 mJ/cm3 for a 12.6 K temperature excursion and a 28-kV/cm electric field excursion).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336244
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  • 6
    Electronic Resource
    Electronic Resource
    High electric field resistivity and pyroelectric properties of vinylidene fluoride-trifluoroethylene copolymer (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 2854-2860 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Copolymers of vinylidene fluoride-trifluoroethylene P(VDF-TrFE) exhibit large piezoelectric and pyroelectric effects. In addition to the most common application of the pyroelectric effect (radiant detection) it is possible to convert heat directly into electrical energy by pyroelectric conversion. This study reports the first measurements of high (constant) field pyroelectric effects of P(VDF-TrFE) which are relevant to pyroelectric conversion. Electric displacement changes which result from temperature changes of the copolymer were measured for thermal cycling from room temperature to 90 °C at fields up to 1 MV/cm. The displacement changes (0.1–0.3 μ C/cm2) were dependent upon the molar ratio of the constituent monomers. The resistivity of the copolymer was also measured in the temperature range 20 to 90 °C and was found to vary from 1012 to 1016Ω cm depending on monomer ratio, temperature, field, and time. The resistivity and displacement change data are discussed in terms of predicted pyroelectric energy conversion performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335857
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  • 7
    Electronic Resource
    Electronic Resource
    Semiclassical quantization of a nonintegrable system: Pushing the Fourier method into the chaotic regime (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7763-7778 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Semiclassical Einstein–Brillouin–Keller (EBK) quantization of the nonintegrable Hénon–Heiles Hamiltonian succeeds using the Fourier transform method of Martens and Ezra. Two innovations are required for this success: (1) the use of tunneling corrected quantizing actions obtained from an approximate, one-dimensional Hamiltonian and (2) exploitation of intermediate-time approximate quasiperiodicity or "vague tori'' wherein the Fourier transform of chaotic motion over 10–100 vibrational periods allows the determination of frequencies and amplitudes which approximate motion during the time interval. Approximate tori, actions, and EBK energy levels are then straightforward. We use an interpolation method to smooth over small resonance zones that are not expected to be important quantum mechanically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468267
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  • 8
    Electronic Resource
    Electronic Resource
    Intramolecular energy transfer in the HNC/HCN isomerization reaction: Quasiclassical state specific isomerization rates controlled by localized potential features (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4452-4460 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model of the HCN molecule with two degrees of freedom, consisting of the H–NC stretch and the H–NC bend with the C≡N distance held fixed, was studied. The semiclassical technique of adiabatic switching was used to obtain trajectories at eigenvalues of metastable states of the system. Quasiclassical results for the isomerization rate from HNC to HCN at various stretch and bend excitations are given. Results show that the isomerization rate is highly dependent on the bend excitation and less so on the total energy of the system in contradiction to predictions of statistical theories. Examination of individual trajectories and surfaces of section reveal the development of chaos near the Nbend =6 level. The development of chaos is apparently responsible for the energy transfer between the modes and thus the isomerization rate. Examination of the potential surface reveals a distinct topological change near the Nbend =6 level. The region responsible for energy transfer is identified, and the possible mechanisms for this transfer are enumerated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452719
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  • 9
    Electronic Resource
    Electronic Resource
    Reply to Comment on "Decoupling of the local mode stretching vibrations of water through rotational excitation. I. Quantum mechanics'' (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7254-7254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454334
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  • 10
    Electronic Resource
    Electronic Resource
    Decoupling of the local mode stretching vibrations of water through rotational excitation. I. Quantum mechanics (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4949-4957 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We demonstrate that in a previously studied model of the stretching modes of the water molecule rotational motion in the plane of the molecule tends to decouple the stretches. For rotational angular momentum near J=18 (h-dash-bar), the two local mode stretches are almost entirely decoupled. The source of this decoupling is the centrifugal distortion which stabilizes the asymmetric stretch and effectively cancels the G-matrix coupling. This cancellation is clarified using three different methods: Direct examination of the numerically computed matrix elements, exact analytic matrix elements of an approximate Hamiltonian, and solutions of a Mathieu equation formulation of a classical resonance Hamiltonian. The importance of this result is discussed in light of the fact that strong rotational excitation can occur in infrared multiple photon excitation. If such rotational decoupling occurs in real systems, then intramolecular energy transfer would be diminished thus holding open the possibility of mode specific infrared excitation. The calculations were carried out by numerically evaluating matrix elements between a basis of Morse oscillator eigenstates using an efficient Gaussian quadrature scheme based on associated Laguerre polynomials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451733
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