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  • 1
    Digitale Medien
    Digitale Medien
    Erratum: Quantization with operators appropriate to shapes of trajectories and classical perturbation theory [J. Chem. Phys. 81, 5013 (1984)] (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 4724-4724 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.450863
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  • 2
    Digitale Medien
    Digitale Medien
    Semiclassical quantization of slightly nonresonant systems: Avoided crossings, dynamical tunneling, and molecular spectra (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 308-318 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: An important problem in the spectroscopy of isolated molecules is the passage of a system through an isolated internal nonlinear resonance as the total energy is changed. The spectral signature of such a passage may involve an avoided crossing together with pre-resonant attraction and/or post-resonant repulsion of levels. While most previous semiclassical studies have made a clear distinction between resonant and nonresonant problems, we develop an approach which allows for a quantitative description of the passage through an avoided crossing which levels may experience as the total energy of the molecule (as opposed to an external perturbation parameter) is varied. Stimulated by the quantum mechanical and time dependent classical studies of Heller and co-workers we have developed a time independent semiclassical formalism which is found to provide excellent quantitative agreement with quantum energy levels and splittings as the total energy is changed. The time independent semiclassical approach provides large savings in computational effort as compared to quantum calculations while providing the quantitative agreement with quantum results which is difficult to obtain from time dependent semiclassical studies. Application is made to nearly resonant 1:1 and 2:1 (Fermi resonant) systems and implications for dynamical tunneling in large molecules are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.451657
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  • 3
    Digitale Medien
    Digitale Medien
    Classical dynamics of intramolecular energy flow and overtone-induced dissociation in HO2H and HO2D (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5791-5804 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A detailed classical trajectory study of the overtone-induced dissociation of hydrogen peroxide HO2H and its isotopic variant HO2D is presented. The factors affecting intramolecular energy flow, such as nonlinear resonances and the various couplings, are examined in detail. The dissociation lifetimes are found to be on the order of picoseconds and comparable with statistical lifetimes, although the intramolecular energy redistribution is not complete within the lifetime of the molecules. Lifetime broadening contributes very little to the rather large width of the overtone excitation feature, which we conclude is in the main inhomogeneously broadened by rotational structure instead. The implications of our results are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.451541
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  • 4
    Digitale Medien
    Digitale Medien
    Unimolecular dissociation in the regular regime (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1135-1144 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The unimolecular dissociation of a model triatomic molecule is analyzed. The model, which is loosely based on the radical HO2, shows mostly regular dynamical behavior although it has enough energy to dissociate. By analyzing the progress towards dissociation, we find that dissociation takes place due to concerted and correlated motions as in the Slater theory of unimolecular reactions rather than the steady accumulation of energy in the dissociative mode.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465411
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  • 5
    Digitale Medien
    Digitale Medien
    Deterministic diffusion in almost integrable systems (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 6 (1996), S. 519-527 
    Details
    ISSN: 1089-7682
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Diffusion processes are usually associated with randomness in the system. In this paper we show that deterministic diffusion processes can also occur in systems with zero entropy that mimic chaos with any precision without being mathematically chaotic. A random walk model is used to predict the behavior of the diffusion coefficient. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.166199
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  • 6
    Digitale Medien
    Digitale Medien
    Competition between adsorbate fragmentation and desorption on laser-heated surfaces (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5059-5068 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We present a theoretical study of the consequences of rapid laser heating of a model adsorbate–substrate system. The adsorbate in this study contains one weak bond and a number of strong bonds. The impetus for our theoretical model comes from the desorption/dissociation experiments on labile organic molecules adsorbed on heated surfaces. Among the numerous interesting results of these experiments are nonstatistical processes where depending on the heating rate, stronger bonds break before the weaker ones. We model these processes by means of a stochastic trajectory approach using the generalized Langevin method. Results are given for model polyatomics of different lengths and configurations as well as different heating rates. The strengths of the weak bonds inside the molecule are changed and reactivities of adsorbates in parallel and perpendicular adsorption geometries are contrasted. The branching ratio between desorption and dissociation is found to depend sensitively on a number of these variables. We also find that small changes in the relative bond strengths of the weak bonds can change the reactivity from statistical to nonstatistical.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464960
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  • 7
    Digitale Medien
    Digitale Medien
    Desorption of vibrationally excited adsorbates in competition with relaxation: A quantal picture (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4400-4412 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The competition between desorption and relaxation of vibrationally excited CO adsorbed on a series of model surfaces is examined theoretically using a quantum mechanical description of the dynamics. This study complements that reported in the preceding paper which studied the classical mechanics of these processes. Quantitative differences between the quantal and classical results are seen in the rate constants for the various energy transfer processes. Moreover, qualitative differences are seen in the trend in the dynamics as the Debye frequency of the model surface is increased. The differences in the various rate constants in the quantal and classical calculations lead to an unusual "quantum effect'' in which the trend in the energy flow with increasing Debye frequency is in different directions. Relaxation of the excited adsorbate is the dominant trend in the classical mechanics; thermal desorption of the excited adsorbate is the dominant trend in the quantal calculations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458723
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  • 8
    Digitale Medien
    Digitale Medien
    Generalizing the Chirikov paradigm: A geometrical view (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 219-225 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The Chirikov pendulum is the standard Hamiltonian of nonlinear dynamics. While many resonant problems of this rich field can be mapped onto this paradigm, the accuracy of its predictions depends on the coupling strengths in the problem. In this article, we generalize the Chirikov pendulum by introducing an alternative reduction, namely to an asymmetric rotor. We also present a geometrical interpretation of both mappings, which is found to be helpful in displaying the dynamics, in particular local and normal mode formation in nonlinear oscillator systems. Our mapping proceeds by finding the Lie algebra for the particular resonance involved, and interpreting its generators as angular momentum components that generate a "constant energy surface'' in three dimensions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.457509
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  • 9
    Digitale Medien
    Digitale Medien
    Intramolecular vibrational energy flow induced by potential and Coriolis couplings (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3159-3170 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The classical dynamics of intramolecular energy flow caused by potential and Coriolis couplings is studied in various representations. The mapping of the problem onto a perturbed asymmetric rotor is found particularly useful. This representation shows the origin of localization/delocalization of energy as well as factors that determine periodic energy exchange. Good agreement is found between the predictions and numerical calculations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455866
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  • 10
    Digitale Medien
    Digitale Medien
    Desorption of vibrationally excited adsorbates in competition with relaxation: A classical picture (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4383-4399 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The competition between desorption and relaxation of vibrationally excited CO adsorbed on a series of model surfaces is examined theoretically using a classical mechanical description of the dynamics. The analogy between these processes and the vibrational predissociation of van der Waals molecules in the gas phase is emphasized. This study, which is restricted to a collinear arrangement of the adsorbate and surface atoms explores the effect of a systematic variation of the parameters of the simple model systems. The parameters varied include the surface Debye frequency and the strength of the adsorbate–surface interaction. Rate constants for the competing processes of predesorption, relaxation, and thermal desorption of both excited and relaxed adsorbate molecules are extracted as a function of the parameter values. Surface vibrations in models of NaCl and Si were found to accelerate the classical predesorption rate compared to the case of a stationary surface. This effect can be rationalized in terms of an impulsive collision mechanism. Raising the surface Debye frequency was found to enhance relaxation at the expense of predesorption. Mode mixing between adsorbate and surface modes appears to be a more important factor in this regard than Fermi resonance, or mode matching. Thermal desorption was not found to be a significant process in these classical calculations. Comparisons with parallel quantal calculations are made in the following paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458722
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