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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5102-5107 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electrochemical techniques are applied to a study of selected intrinsic physical properties (independent of dopant) of polyacetylene, (CH)x. Electrochemical voltage spectroscopy (EVS) is used to characterize the energies of charge injection and removal for both cis-(CH)x and trans-(CH)x. The difference in charge injection and ejection potentials is shown to give a direct measure of the approximate semiconductor band gap and the results are compared with similar data from optical measurements. Charge injection and ejection potentials are used to define the redox potentials of (CH)x and are used in conjunction with equilibrium potential measurements at varying oxidation or reduction levels of polyacetylene to present a unifying concept to the electrochemistry of (CH)x.
    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 89 (1988), S. 3057-3062 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A nonperturbative theory of predissociation based upon an effective Hamiltonian is presented. For a model diatomic system in which a (bound-state) Morse potential-energy curve is crossed by an (unbound-state) exponential potential-energy curve, the exact effective Hamiltonian may be obtained in high precision for any well behaved interaction potential. The real and imaginary parts of the eigenvalues of the effective Hamiltonian give the (shifted) energies and widths, respectively, of the predissociative states. Numerical results are obtained and compared with both a semiclassical approximation and those derived from solutions of coupled Schrödinger equations. In the weak-coupling regime the agreement between the present method and semiclassical results is good, and better in general than the coupled-equations results, which apparently suffer from instability problems. For couplings of intermediate strength, the semiclassical method breaks down, as do fully quantum-mechanical first-order perturbation approximations, as is demonstrated by comparison with the converged nonperturbative results. Fixed points of the spectrum appear at "resonance'' values of the coupling strength which bring the exact energy eigenvalue into resonance with one of the adiabatic levels so that the imaginary part (level width) of the former vanishes. Thus beyond a critical coupling strength, stronger coupling enhances the stability of a resonance.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5984-5985 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nature of the metastable state of hydrogen trimers described by Ga and Kuppermann (ref.1) is further discussed. The analysis is based on linewidth measurements in the emission spectrum of the trimer, the quantum mechanical selection rules, and earlier beam and photoionization measurements.(AIP)
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7662-7670 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Formulation of the expectations of eight operators required for the evaluation of the Born corrections, the Born couplings, and higher derivatives of the Born–Oppenheimer wave functions are derived for the case of a Gaussian-lobe orbital (GLO) basis. The relative simplicity of these analytical formulas is a special advantage of GLO and reduces the computer time in these calculations. Some operators treated here require a modification of the Slater rules. As examples of applications of these techniques, ab initio calculations of the orbital stresses and the Born corrections for the ground state X 1Σ+g and excited states 1Σ+g(II), C, C' 3Πu, and 3Πu(II) of N2 are reported. The obtained results show that the Born correction near the avoided crossing region strongly depends upon the nuclear separation; in this region configuration interaction makes an important contribution.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4949-4956 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nuclear displacement operator (NDO) for Born–Oppenheimer electronic wave functions (BOEWF) is introduced and some recurrence formulas are obtained. The formulas for Born couplings and higher derivatives of BOEWF with respect to nuclear coordinates are derived from very general considerations and relations among these quantities are given. The series form, exponential, and integral forms of the NDO are exhibited. Particularly, it is proven that for the two-state systems the NDO has a very simple form by which it is convenient to study two-state dynamical processes. It is shown that the NDO satisfies a differential equation which is analogous to that for the time-evolution operator in the presence of a time-dependent perturbation. The physical meanings of these two operators are compared. It is demonstrated that the NDO is uniquely determined by the vector Born coupling matrix, and that the nuclear motion may be analyzed in terms of a local non-Abelian gauge transformation.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 3646-3649 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Final state distributions and state-specific reaction cross sections for 1.5–6 keV He2+/K collisions have been determined from data acquired using both neutralized ion beam spectroscopy and direct observation of luminescence from decay of excited collision products. While several minor reaction channels can be identified, it is found that near-resonant processes yielding He2(a 3Σu+) and He2(A 1Σu+) are predominant. These major channels, both of which have cross sections in excess of 100 A(ring)2, lead to substantial production of energetic metastable molecules and VUV continuum radiation extending from about 750 to 850 A(ring).
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4916-4919 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relative abundances of metastable H@B|3 and D*3 molecules in collimated beams of neutralized ions are analyzed by the technique of collisional reionization (charge stripping). The fraction of metastable/dissociative species formed in the electron transfer process H+3(D+3)+K(g) → H@B|3(D*3)+K+ diminishes if the precursor ions have excess internal energy. The abundance ratio of H@B|3/D*3 for equivalent 6 keV beam fluxes increases sharply when the time span between neutralization and reionization is increased. The measurements show that a state of D@B|3 with low rotational quantum numbers (N〉0) is decaying on the time scale of the beam transit with a lifetime of about 0.2 μs. Results are interpreted in reference to the predissociation behavior of the 2p 2A2 electronic state of the radical. The disproportionate ratio of IH@B|3/ID*3 (very-much-greater-than) 1 is a consequence of the relative abundances of precursor levels in H+3 and D+3 that can transform into metastables by electron transfer.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 7795-7804 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the efficient construction of guiding wave functions for use in diffusion Monte Carlo calculations of electronic excited states. We test guiding wave functions obtained from singles-only configuration interaction, time-dependent density functional theory, and complete active space self-consistent field methods. The techniques are used to study the first ionization potentials and excited states of silane and methane. © 2001 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1494-1500 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electron energy analyzer which acts as a bandpass filter while maintaining the spatial integrity of an electron image in a uniform magnetic field is described. It embodies some new electron-optical properties. Image electrons injected parallel to the magnetic field are guided, using crossed electrostatic and magnetic fields, to a low-pass electron mirror and then through a high-pass retardation filter. Nonuniform electrostatic deflection fields are used to compensate for the energy-dependent dispersion of the crossed fields. A simple computer modeling method used to design the electrostatic fields is described. A test analyzer was constructed to operate in a 0.0125-T (125 G) uniform magnetic field to investigate its properties. Bandpass filtered images of an 18-eV electron source demonstrating the removal of energy-dependent dispersion and the narrowing of the bandwidth to 100 meV are presented. Another application of the analyzer, to obtain an energy spectrum from a spatially extended electron source, is demonstrated.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2012-2015 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A technique is described to determine the spatial x-ray flux emitted from a hohlraum wall and subsequently transmitted through a diagnostic hole. This technique uses x-ray diodes, bolometers, and a time-resolved pinhole camera to determine the spatial flux of x rays emitted through a hohlraum's diagnostic hole. The primary motivation for this analysis was the relatively long duration, nearly 100 ns, of the x-ray drive present in z-pinch driven hohlraums. This radiation causes plasma to ablate from the hohlraum walls surrounding the diagnostic hole and results in a partial obscuration that reduces the effective area over which diagnostics view the radiation. The effective change in area leads to an underestimation of the wall temperature when nonimaging diagnostics such as x-ray diodes and bolometers are used to determine power and later to infer a wall temperature. An analysis similar to the one described below is then necessary to understand the radiation environment present in x-ray driven hohlraums when these diagnostics are used and hole closure is important. © 1999 American Institute of Physics.
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