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  • 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
    Use of Kramers–Kronig transforms for the treatment of admittance spectroscopy data of p-n junctions containing traps (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7830-7836 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of Kramers–Kronig transforms is proposed for the treatment of admittance spectroscopy data of junctions when significant shunt conductance or series resistance is present. An algorithm has been implemented to calculate the transformations numerically and the validity of the method developed has been tested using simulated data. Two experimental systems, p-n junctions into InP made by ion implantation, and atomic-layer-epitaxy-grown CdS/CdTe heterojunctions, have been characterized using this procedure. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362391
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  • 3
    Electronic Resource
    Electronic Resource
    CuInSe2 thin films produced by rf sputtering in Ar/H2 atmospheres (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4163-4169 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Structural, compositional, optical, and electrical properties of CuInSe2 thin films grown by rf reactive sputtering from a Se excess target in Ar/H2 atmospheres are presented. The addition of H2 to the sputtering atmospheres allows the control of stoichiometry of films giving rise to remarkable changes in the film properties. Variation of substrate temperature causes changes in film composition because of the variation of hydrogen reactivity at the substrate. Measurements of resistivity at variable temperatures indicate a hopping conduction mechanism through gap states for films grown at low temperature (100–250 °C), the existence of three acceptor levels at about 0.046, 0.098, and 0.144 eV above valence band for films grown at intermediate temperature (250–350 °C), and a pseudometallic behavior for film grown at high temperatures (350–450 °C). Chalcopyrite polycrystalline thin films of CuInSe2 with an average grain size of 1 μm, an optical gap of 1.01 eV, and resistivities from 10−1 to 103 Ω cm can be obtained by adding 1.5% of H2 to the sputtering atmosphere and by varying the substrate temperature from 300 to 400 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339135
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  • 4
    Electronic Resource
    Electronic Resource
    Role of deep levels and interface states in the capacitance characteristics of all-sputtered CuInSe2/CdS solar cell heterojunctions (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3236-3241 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: All-sputtered CuInSe2/CdS solar cell heterojunctions have been analyzed by means of capacitance-frequency (C-F) and capacitance-bias voltage (C-V) measurements. Depending on the CuInSe2 layer composition, two kinds of heterojunctions were analyzed: type 1 heterojunctions (based on stoichiometric or slightly In-rich CuInSe2 layers) and type 2 heterojunctions (based on Cu-rich CuInSe2 layers). In type 1 heterojunctions, a 80-meV donor level has been found. Densities of interface states in the range 1010–1011 cm2 eV−1 (type 1) and in the range 1012–1013 cm−2 eV−1 (type 2) have been deduced. On the other hand, doping concentrations of 1.6×1016 cm−3 for stoichiometric CuInSe2 (type 1 heterojunction) and 8×1017 cm−3 for the CdS (type 2 heterojunction) have been deduced from C-V measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342676
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  • 5
    Electronic Resource
    Electronic Resource
    Structural, electrical, and optical properties of CuGaSe2 rf sputtered thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 189-194 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of CuGaSe2 have been produced by rf sputtering. Compositional, structural, electrical, and optical properties are strongly influenced by growth temperature. At substrate temperatures lower than 300 °C amorphous or poorly crystalline Se-excess films are obtained, showing high resistivity (≈103 Ω cm) and optical transitions at 1.62, 1.80, and 2.4 eV (values lower than the single-crystal counterparts). At the higher growth temperatures, polycrystalline films are obtained (average grain size 0.7 μm) with lower values of resistivity (1 Ω cm), and optical transitions at 1.68, 1.90, and 2.55 eV (very close to the single-crystal values). A hopping conduction mechanism has been detected at the lower measuring temperature (T〈150 K), and a grain boundary limited conduction process at the higher measurements temperature (T〉150 K). Structural and compositional characteristics are used to explain the behavior observed in the electrical and optical properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347113
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  • 6
    Electronic Resource
    Electronic Resource
    Semiclassical vibrational energies and transition frequencies for a Hamiltonian with stretch–bend potential energy coupling: Application of Fourier methods (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6609-6617 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Semiclassical methods are applied to determine transition frequencies and vibrational energies for the two-mode HC2 stretch–bend Hamiltonian recently studied by Swamy and Hase [J. Chem. Phys. 84, 361 (1986)]. The mean action spectral approximation for calculating transition frequencies is found to give results in excellent agreement with quantum variational values. The FFT EBK method is used to calculate vibrational eigenvalues for both nonresonant and 3:1 resonant states. Both approaches give results more accurate than those reported by Swamy and Hase using the DeLeon–Heller–Miller method. The presence of stretch–bend potential coupling is found to reduce the extent of classical chaos.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453445
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  • 7
    Electronic Resource
    Electronic Resource
    MC test of perturbation theories based on site–site potentials (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2445-2452 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The extension of the Barker–Henderson (BH) theory to diatomic potentials is examined by comparison of the predicted thermodynamic properties with "exact'' MC results. Two choices of the potential separation have been considered; corresponding to the BH scheme and that of Weeks–Chandler–Andersen (WCA). Attention has been paid to the effect of the usual approximations to the exact properties of the hard reference system (equation of state and pair correlation functions) and to the convergence rate of the expansion. Conclusions can also be drawn for the extension of the WCA-blip function theory to these systems. It is shown that the behavior of the perturbation expansions exhibits the same features observed in atomic fluids. Nevertheless, the presence of the molecular anisotropy leads to a rather different assessment of the relative usefulness of each theory. Incidentally, small inaccuracies of the well-known Boublik and Nezbeda equation for the compressibility factor of dumbbells have been discovered at very high densities (outside the range previously reported).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448288
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of intermolecular potential model on the structure and conformational equilibrium of liquid n-butane (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 297-306 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Several Monte Carlo simulations with a sample of 125 molecules of n-butane with four Lennard-Jones centers and internal rotation, have been carried out by varying the values of ε and σ parameters of the intermolecular potential. In this way the effect of such changes on the thermodynamic, structural, and conformational properties have been studied. Although the structure remains practically unaffected by moderate variations in the Lennard-Jones parameters, nevertheless the conformational equilibrium is very sensitive to them. Also specific properties of chain molecules in the n-butane, such as the effect of the relative position of centers (external vs internal ones) and the possibility of orientational correlation have been explored. The difference between the effects of the external centers vs the internal ones can be quantified and it turns out to be significant; on the other hand the orientational correlation is very weak at room temperature and normal liquid density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449823
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  • 9
    Electronic Resource
    Electronic Resource
    Transferring vibrational population between electronic states of diatomic molecules via light-induced-potential shaping (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8820-8830 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate two-photon, selective excitation of diatomic molecules with intense, ultrafast laser pulses. The method involves transfer of a vibrational population between two electronic states by shaping of light-induced potentials (LIPs). Creation and control of the LIPs is accomplished by choosing pairs of transform-limited pulses with proper frequency detunings and time delays. Depending on the sequence of pulses (intuitive or counter-intuitive) and on the sign of the detuning (below or above the first transition) four schemes are possible for population transfer by LIP shaping. We develop a simple analytic model to predict the optimal laser pulses, and to model the adiabatic dynamics in the different schemes. Based on a harmonic, three-state model of the sodium dimer we demonstrate numerically that all four schemes can lead to efficient, selective population transfer. A careful analysis of the underlying physical mechanisms reveals the varying roles played by the adiabatic and diabatic crossings of the LIPs. The detailed mechanisms influence the robustness and experimental applicability of the schemes. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1368130
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  • 10
    Electronic Resource
    Electronic Resource
    Sensitivity of intramolecular vibrational energy relaxation to stretch–bend potential energy coupling and stability of periodic orbits (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 801-811 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Stretch–bend coupling via 2:1 Fermi resonance is an important mechanism for rapid energy flow from overtone excited CH local mode states. To elucidate the role of potential energy coupling, we have studied the classical dynamics of a two-mode stretch–bend Hamiltonian for the benzene fragment C3 H. The effects of attenuation of the CCH bend force constant by stretching of the CH bond on the short time (up to 0.12 ps) probability decay dynamics of the model system are in good qualitative accord with trends found previously in full scale classical trajectory simulations on planar benzene by Lu, Hase, and Wolf. Surfaces of section are used to study the classical phase space structure of the stretch–bend Hamiltonian. A close correlation between instability of the CH periodic orbit and exponential decay of probability is found, and relaxation rates can be estimated to good accuracy by linear stability analysis of the periodic orbit. Increasing the strength of the potential coupling stabilizes the CH periodic orbit, thereby suppressing overtone relaxation. There is therefore an effective cancellation of kinetic and potential stretch–bend coupling terms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455203
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