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  • 1985-1989  (20)
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Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Effects of the transition dipole in Raman scattering (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 7107-7119 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100357a019
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    On the relationship between the classical, semiclassical, and quantum dynamics of a Morse oscillator (1988)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 92 (1988), S. 3225-3235 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100322a034
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Hybrid mechanics. II (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7317-7329 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We recently published a new method for the calculation of the time evolution of a wave function. We used an accurate approximate method to calculate the time propagator for a finite time Δt. Numerical calculations showed that this scheme works quite accurately, but that it is not more efficient than conventional methods. In this paper we propose to use a very fast and simple, but less accurate semiclassical method for the calculation of the time propagator. The approximation consists in the replacement of the Hamiltonian by a quadratic approximation around the center of the evolving wave packet called thawed Gaussian dynamics. We show by numerical examples in one and two dimensions that, despite this crude approximation, we achieve nearly the same accuracy as in the foregoing paper, but with an efficiency that is typically more than an order of magnitude better. We further show that the method is able to describe tunneling and long time dynamics (e.g., 1000 vibrational periods).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456211
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Cross section and optical theorem for defects on a corrugated surface (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2550-2557 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The definition for the surface scattering cross section of an object (defect, adatom, etc.) on a periodic surface in three dimensions is given. The analog of the Optical Theorem for gas phase scattering is derived. Calculations (made using semiclassical wave packets) are reported and compared to experiments for CO on Pt(111).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455050
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum dynamics for vibrational and rotational degrees of freedom using Gaussian wave packets: Application to the three-dimensional photodissociation dynamics of ICN (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4700-4713 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an approach to quantum dynamics, based entirely on Cartesian coordinates, which covers vibrational as well as rotational motion. The initial state is represented in terms of multidimensional Gaussian wave packets. Rotational adaptation to angular momentum eigenstates is done by using angular momentum projection operators. This gives an initial state represented as a weighted superposition of Gaussians with different average orientation in space. It is shown that the subsequent dynamics can be determined from the dynamics of Gaussians corresponding to just one of these orientations. An application to the 3D photodissociation dynamics of ICN is presented. All six degrees of freedom which describe the internal motion of the triatomic are included, the only approximation introduced in the present calculation being the thawed Gaussian wave packet approximation for the dynamics. The total absorption spectrum out of vibrational–rotational eigenstates of ICN as well as fully resolved final product distributions are calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456759
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Hybrid mechanics: A combination of classical and quantum mechanics (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4752-4760 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Because classical mechanics is so much easier to handle than quantum mechanics, the time evolution of wave functions for molecular dynamics is often calculated using semiclassical methods. The errors of such methods grow, in general, faster than linearly with time, although they may be quite small for small, but finite times. We therefore propose to use a semiclassical method to calculate the quantum mechanical time propagator for a finite time step (say 1/10 of a vibrational period) and to use this propagator and quantum mechanics for longer times. To describe the quantum time propagator we use a basis set that can describe regions in phase space that are not necessarily rectangular, but can have any shape, that will become important in applications to higher dimensions. We give numerical examples to demonstrate the accuracy of the method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455669
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    CH2I2 photodissociation: Dynamical modeling (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3602-3611 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A full quantum mechanical calculation is carried out on the first excited state of CH2I2 to model the absorption and emission spectra and examine the photodissociation dynamics from a time dependent point of view. The dissociation at 355 nm is direct in the sense that the wave packet does not revisit the Franck–Condon region. The initial motion of the excited molecule is mainly along the CI2 symmetric stretch coordinate while simultaneously spreading in the antisymmetric stretch coordinate. The molecule then dissociates along a C–I "local'' mode; no I2 can be formed in this energy region. Vibrationally hot CH2I radical in the C–I mode is predicted. The model is in good agreement with available experimental results. A simple and intuitive method is presented to construct model potential energy surfaces for two chromophore systems from the potential energy surface and information known for the corresponding single chromophore. CH3I and CH2I2 are used as numerical illustrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454880
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Ring torsional dynamics and spectroscopy of benzophenone: A new twist (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2169-2184 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low energy portion of the high resolution S1←S0 fluorescence excitation spectrum of benzophenone recently reported by Holtzclaw and Pratt [J. Chem. Phys. 84, 4713 (1986)] is modeled here using a simple two-degree-of-freedom vibrational Hamiltonian. The Hamiltonian features a 1:1 nonlinear resonance between the two low frequency ring torsional modes of the molecule in its S1 state. Line positions and intensities of the two major spectral progressions are well reproduced using parameters similar to those derived from earlier matrix diagonalizations. The comparison of the theory and experiment results in a determination of the displacement of the S1 surface relative to the ground electronic state along the symmetric torsional coordinate and permits a calculation of the excitation spectra of various isotopically substituted molecules not yet measured in the laboratory. A clear picture of the relationship between the dynamics on the S1 surface and the spectroscopy of benzophenone is revealed by comparing a time domain analysis of the experimental data with wave packet dynamics on the model S1 surface. This comparison provides new insight into energy flow in the isolated molecule and permits a qualitative simulation of the effects of collisional quenching on the fluorescence spectrum. We also discuss, using a classical trajectory analysis, the resonance dynamics of the torsional modes and note the existence of heretofore undetected local modes in the high resolution spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454050
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Generalized Gaussian wave packet dynamics, Schrödinger equation, and stationary phase approximation (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2003-2014 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have recently published a new semiclassical method, generalized Gaussian wave packet dynamics, which extends Gaussian wave packet dynamics into complex phase space. Although we were able to give an accurate formulation of the method, we had at the time of writing that paper only an intuitive, heuristic understanding of the deeper causes which make the method work. A more mathematical understanding was needed. To close this gap we show in this paper the equivalence of the new method with a first order expansion of (h-dash-bar) of the Schrödinger equation. We further prove that the new method is equivalent to the stationary phase approximation, using the usual WKB formula for the propagator. The latter equivalence enables us to show that all the symmetry properties of time-dependent quantum mechanics also hold in the new semiclassical theory. Finally, we provide some elaboration of the method, and clarify several issues that were not discussed before. With this new insight we are able to formulate a simple rule for the calculation of semiclassical wave functions that contain contributions from more than one branch. This corrects for the divergence of semiclassical wave functions near caustics, a problem that we encountered in the preceding paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455714
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Simplifying the MIME: a formula relating normal mode distortions and frequencies to the MIME frequency (1987)
    s.l. : American Chemical Society
    Inorganic chemistry 26 (1987), S. 2158-2160 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00260a029
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    Paper (German National Licenses)
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