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  • 1
    Digitale Medien
    Digitale Medien
    Molecular hyperfine structure in the photoassociation spectroscopy of laser cooled atoms (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2634-2637 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The photoassociation of colliding ultracold trapped atoms permits the observation of high resolution molecular spectra of high lying vibrational levels with low total angular momentum and outer turning points greater than 50 A(ring). This paper describes how the hyperfine structure of alkali dimer molecules at large internuclear separation can be used to assign the electronic character of the observed photoassociation spectra and how hyperfine structure helps to explain the observed photoassociation spectrum of the attractive electronic states of the Na2 molecule that correlate with Na(3 2S)+Na(3 2P3/2) atoms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.467637
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  • 2
    Digitale Medien
    Digitale Medien
    Three-dimensional analytical quantum mechanical theory for triatomic photodissociation: Role of angle dependent dissociative surfaces on rotational and angular distributions in the rotational infinite order sudden limit (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5456-5478 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: An analytical quantum mechanical model is developed for calculating fragment energy distributions in photodissociation of linear triatomic molecules when the repulsive potential energy surface is anisotropic. The translational continuum function is taken to be given by the infinite order sudden approximation, but an equivalent adiabatic interpretation leads to a natural choice for the diatomic angular momentum j and for the retention of asymptotic rotational energy differences. Normal coordinates are used for the initial bound state before dissociation, while scattering coordinates are applied for wave functions on the dissociative surface. These natural choices lead to three-dimensional nonseparable bound–continuum transition amplitudes. The translational continuum wave function is further approximated using Airy functions, and additional approximations are introduced based on the presence of small amplitude vibrations in the initial bound state. The three-dimensional transition amplitudes are then analytically reduced to sums of one-dimensional quadratures. The theory has been applied to the photodissociation of several rovibronic states of N2O+(A˜ 2∑+) (predissociation) and ICN(C˜ 1A') (direct photodissociation), and the rotational distributions for J=0 are in good agreement with three-dimensional close-coupled calculations except when the potentials become highly anisotropic. Our photodissociation infinite order sudden approximation is tested against various versions of the rotational infinite order sudden approximation for N2O+ and are found to be in good agreement with previous results. The present theory readily permits calculations for J〉0 and may be used for the calculation of rotational distributions for excited rotational and/or vibrational states. In the limit of isotropic potentials the remaining integrals are evaluated to provide analytical approximations for the transition amplitudes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.452570
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  • 3
    Digitale Medien
    Digitale Medien
    Dynamics and spectroscopy of near threshold nonadiabatic resonances in photodissociation to open shell atoms: CH+ a model system (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2699-2717 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Close-coupled theoretical calculations of the near threshold photodissociation of CH+ exhibit a wealth of structure. This structure arises because of the presence of nonadiabatic interactions which always exist and which are significant at large distances when molecules dissociate to open shell atoms. Detailed analysis of the calculated photodissociation spectrum, using an extensive set of theoretical diagnostics, displays a series of systematic trends in the spectrum which enable the assignment of resonance features in this extremely complicated spectrum. The results show how general spectroscopic principles may be used in analyzing this type of complicated structure, and our calculations provide general insight into the experimental data for the photodissociation of CH+. The theoretical calculations also indicate how additional assistance with analyzing experimental data can come from measurements of fragment kinetic energy, angular distributions, and polarizations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.451027
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  • 4
    Digitale Medien
    Digitale Medien
    Close-coupled calculations of resonance widths observed in photodissociation spectra of CH+ (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6070-6076 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The widths of near-threshold resonances observed in photodissociation spectra of CH+ are calculated by a close-coupled method. Potentials are derived from a combination of experimental data and ab initio computations. The results are in good agreement with experiment. Comparison is made with Fermi golden rule perturbative calculations of the resonance widths from the preceding paper (paper I). Calculations are presented for the branching ratio between the spin–orbit states of the C+ fragment that are produced by laser excitation to these resonances and that are yet to be determined experimentally.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456372
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  • 5
    Digitale Medien
    Digitale Medien
    Dynamics of triatomic photodissociation in the interaction representation. I. Methodology (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1721-1737 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: This paper presents a new, quantum mechanical, time dependent approach to the photodissociation of triatomic molecules in Jacobi coordinates. The algorithm is based on a nested interaction representation, designed to make the representation of the time evolving wave packet as compact as possible. The new equations of motion are solved numerically using a synthesis of grid techniques: the fast Fourier transform (FFT) method is used in Cartesian-like coordinates, and the discrete variable representation (DVR) method in the angular or bending coordinate. A variant on the short iterative Lanczos (SIL) procedure is used for the temporal propagation of the wave packet. Rotational state distributions obtained from this new algorithm are presented for the single surface photodissociation of ClCN and for the two surface photodissociation of ICN. The ClCN results are in good agreement with the semiclassical results of Barts and Halpern [J. Phys. Chem. 93, 7346 (1989)] and in excellent agreement with the time independent quantum results of Schinke [J. Chem. Phys. 92, 2397 (1990)]. Rotational state distributions for the two electronic surface photodissociation of ICN are in good agreement with the time independent quantum results of Guo and Schatz [J. Chem. Phys. 92, 1634 (1990)] and illustrate the flexibility of the method for dealing with nonadiabatic processes. The numerical efficiency of the method is comparable with standard time independent techniques, but has the attractive feature of yielding final state distributions at all energies from a single wave packet propagation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461022
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  • 6
    Digitale Medien
    Digitale Medien
    Three-dimensional analytic quantum theory for triatomic photodissociations. II. Angle dependent dissociative surfaces and rotational infinite order sudden approximation for bent triatomics (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7283-7301 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We extend to triatomic molecules with bent initial bound states our analytical quantum theory of triatomic photodissociations. The theory uses basis functions for the initial bound state wave function that are product functions in the natural normal (or local) modes appropriate to that state and a continuum wave function that is a product function in the natural scattering coordinates appropriate to the dissociative surface. This choice of wave functions produces three-dimensional nonseparable transition amplitudes which are reduced to analytical forms by introduction of the infinite order sudden and Airy approximations for the continuum wave function and a quadrature formula for the integral over bending motions. The present theory also lifts some assumptions that had been introduced previously to simplify the theory for isotropic repulsive potentials. Thus, we use the exact nonlinear relation between the bound state bending angle and the scattering angle to remove the previous small angle approximation that is shown to lead to inaccuracies in some cases. We also study the ramifications of the fact that the bound state bending vibration is generally a linear combination of pure bend and both bond stretches in the transformation between normal modes and scattering coordinates. Inclusion of this bend–stretch coupling, ignored in our previous analytical work and in many theories of triatomic photodissociation that employ expansions of the bound state wave function in a basis set expressed in dissociative surface scattering coordinates, is shown to have profound influence on computed fragment rotational distributions. The bend–stretch couplings serve often to wash out the additional high frequency oscillations that appear in prior approximate treatments in which these couplings are ignored. This then leads to fragment rotational distributions that contain only those oscillations resulting from the map of the initial bound state bending vibration. Comparison is made with three-dimensional close coupled and DVR calculations for the photodissociation of HCN from the bent C˜1A' state. Calculations are also presented for initial states of high rotational angular momenta.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458214
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  • 7
    Digitale Medien
    Digitale Medien
    Nested interaction representations in time dependent quantum mechanics (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2998-3009 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Two significant developments in the formulation of the equations of motion in the interaction representation (IR) are introduced in this paper. These developments have direct bearing on the efficient propagation in the interaction representation. The first of these developments involves the concept of sequential, or "nested'' interaction transformations on the Hamiltonian and the wave function. Two such nested IRs are described. The first is a momentum- or "P-adapted'' IR which, in addition to removing wave packet spreading, systematically maintains the average momentum 〈P〉 at zero. This facilitates a grid which not only has a minimal range, but whose points are maximally sparse. Evaluating the Hamiltonian operator in the P-adapted interaction representation involves only one simple algorithmic modification to the ordinary IR: replacing eiH0t/(h-dash-bar)V(R)e−iH0t /(h-dash-bar)→eiH0t/(h-dash-bar)V(R+〈P〉t/m) eiH0t/(h-dash-bar), i.e., using the potential energy function which is downstream from the wave function by the classical propagation distance. A PR-adapted IR is also defined, which systematically maintains both the average position 〈R〉 and momentum 〈P〉 at zero.The PR-adapted IR also involves only one modification to the ordinary IR: replacing eiH0t/(h-dash-bar)V(R)e−iH0t /(h-dash-bar)→eiH0t/(h-dash-bar)V(R+〈R〉 +〈P〉t/m)eiH0t/(h-dash-bar). The second formal development consists of the application of the operator equation eiH0t/(h-dash-bar)V(R)e−iH0t /(h-dash-bar)=V(R+Pt/m) in conjunction with the nested IRs. This formal identity, which is essentially the Heisenberg representation for V(R), provides a convenient route to propagation in the interaction representation without reconstructing the Schrödinger wave function as an intermediate. The time propagation in all representations is performed using an iterative Lanczos reduction scheme combined with a second- order Magnus expansion. Numerical results for the exponential and the 1/R potential are presented, and illustrate that the new representations can easily lead to a savings of an order of magnitude in the size of the grid required for the propagation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461997
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  • 8
    Digitale Medien
    Digitale Medien
    Three-dimensional analytical infinite order sudden quantum theory for triatomic photodissociation: Dependence on initial rotational and vibrational state and on thermal averages for NOCl dissociation on T1(1 3A‘) surface (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 9215-9227 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Our previously developed analytical infinite order sudden quantum theory of triatomic photodissociation is generalized to compute fragment internal energy distributions when the initial triatomic rotational state has K≠0. The dependence of product rotational energy distributions on initial rotational and vibrational state is illustrated through model computations for the direct NOCl photodissociation from the ground to the T1(1 3A‘) potential energy surface. The calculations consider all J,K≤9 and employ a repulsive potential that is fit to ab initio computations. Comparisons of fragment rotational distributions with previous semiclassical approximations further elucidate the role of the mapping of the initial state bending wave function onto the fragment rotational distributions and the influence of parent rotations on this mapping. The infinite order sudden quantum-mechanical distributions exhibit a more complex structure, but upon thermal averaging they are already transformed at T=3 K into fairly broad rotational distributions. The present theory readily permits the calculations of energy distributions for initial states of high J and K.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.467257
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  • 9
    Digitale Medien
    Digitale Medien
    SPORES OF CLOSTRIDIUM BOTULINUM IN GEORGIA SOIL (1950)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food science 15 (1950), S. 0 
    Details
    ISSN: 1750-3841
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2621.1950.tb16724.x
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  • 10
    Digitale Medien
    Digitale Medien
    Nonadiabatic effects on the photodissociation of diatomic molecules to open-shell atoms (1987)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 91 (1987), S. 5402-5409 
    Details
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/j100305a005
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