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  • 1
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1905-1916 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of shock wave generation, propagation, and decay in an Ar lattice following photodissociation of an I2 impurity are studied using molecular dynamics simulation. A two-dimensional model is treated to allow the modeling of shock wave propagation over larger distances than easily accessible in full three-dimensional calculations. The shock waves are created on atomic length scales by binary collisions between the nascent photofragments and adjacent lattice atoms, and propagate long distances through the crystal in a highly directed, quasi-one-dimensional manner. As a consequence of the I/Ar mass ratio, the I fragments undergo multiple collisions with the adjacent Ar atoms situated along the I–I bond axis, generating pulse trains of shock waves, each with a characteristic initial energy, velocity, and decay rate. The dynamics of the system are interpreted using a simple one-dimensional hard sphere model. © 1995 American Institute of Physics.
    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 105 (1996), S. 9072-9082 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-dimensional time-dependent wave packet calculations are carried out on a collinear model of the I2(B)–Ar complex to investigate the possible kinematic origin of the one-atom cage effect in small van der Waals molecules. Three different excitation wavelengths are considered (496.5, 488, and 476.5 nm), and the dynamics are assumed to be restricted to the I2 B state electronic surface, with no nonadiabatic transitions following the pump excitation. Good agreement with experiment is obtained. To investigate the sensitivity of observable final state distributions on the weak intermolecular potential between I2 and Ar, three slightly different B state I–Ar interactions are employed for the case of 488 nm excitation. It is found that relatively small changes in the form and magnitude of the weak van der Waals interactions can have a large effect on the final state distributions. These results suggest that the experimental data on I2–Ar photodissociation–recombination can be explained by a purely kinematic one-atom cage effect on the B state electronic surface for a collinear population of I2–Ar clusters, without the need to introduce nonadiabatic electronic effects. © 1996 American Institute of Physics.
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  • 6
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational predissociation dynamics of the van der Waals cluster I2(B,v)–Ar13 are studied theoretically from a classical mechanical perspective. The focus is on the ejection of the first Ar atom from the excited cluster. This process is found to occur by two competing mechanisms (1) evaporation of a cluster atom induced by the slow vibrational relaxation of the I2 impurity, and (2) direct ejection of a geometrically favored Ar atom by two or more impulsive collisions with the vibrating I2. In contrast with the picture of independent binary collisions, the multiple argon–iodine interactions leading to successful direct dissociation are correlated in time. The relative propensity of the direct channel is a highly structured function of v, the initial vibrational level of the I2. This behavior results from the energy-dependent frequencies of motion of the diatomic and the localized Ar cluster mode, and is a novel example of a nonlinear resonance between "system'' and "bath'' degrees of freedom.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7234-7241 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational predissociation dynamics of an Ar13 cluster containing a vibrationally excited I2 molecule in its B electronic state are studied by classical trajectory simulation. The kinetics of the loss of the first Ar atom from the cluster induced by vibrational relaxation of the diatomic exhibits unusual nonexponential behavior, characterized by an instantaneous rate that increases with time. The simulation results are modeled by a hybrid statistical model, which explicitly takes into account the slow relaxation of the impurity while assuming rapid redistribution of energy among the low frequency cluster modes. Minor deviations between the simulation and theory are observed, and indicate nonstatistical effects in the "solvent'' degrees of freedom.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8971-8979 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The representation of the two-dimensional harmonic oscillator by the unitary group SU (2) simple Coriolis-adapted vibrational basis states for the treatment of vibration–rotation interaction in polyatomic molecules. The vibrational part of the zeroth-order vibration–rotation Hamiltonian is expressed in terms of the generators (Sx,Sy,Sz) of the group SU(2), leading to a coupled angular momentum representation of the vibration–rotation Hamiltonian. In the prolate limit, this leads to an effective k-dependent zeroth-order vibrational Hamiltonian that is linear in the group generators. The problem can be solved exactly in this limit by a simple axis transformation in the vibrational "spin'' space. Because of the underlying SU(2) structure, the transformation matrix elements and overlaps of basis states of different effective Hamiltonians corresponding to different values of k are given by simple expressions involving Wigner d matrices.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 284-302 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper addresses the general problem of zeroth order representation of resonant dynamics. We investigate the classical, quantum mechanical, and semiclassical transformation properties of two-dimensional isotropic and anisotropic uncoupled harmonic oscillators. The classical and quantal theories are presented in a manner that emphasizes the strong correspondence between the two, and in particular, the SU(2) symmetry exhibited by both the classical and quantum oscillators. The classical canonical transformations relating the action-angle variables appropriate for normal, local, and precessional motion of the isotropic oscillator are derived by explicit calculation of the generating functions. By employing a simple mapping relating the anisotropic and isotropic oscillators, expressions for action-angle variables appropriate for the topology of an arbitrary m:n resonance are determined. The resulting invariant tori are compared with the corresponding quantum mechanical wave functions and phase space densities. The relationship between the classical and quantum mechanical theories is illustrated by determining semiclassical approximations to the unitary transformation matrix elements, which are given in terms of the classical generating functions. Applications to problems of current interest, such as the adiabatic switching method for semiclassical quantization of nonseparable systems, are briefly discussed.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 7345-7354 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper, we describe the application of our recently developed multistate semiclassical Liouville equation method for modeling molecular dynamics on multiple coupled electronic states [C. C. Martens and J.-Y. Fang, J. Chem. Phys. 106, 4918 (1997); A. Donoso and C. C. Martens, J. Phys. Chem. 102, 4291 (1998)] to problems where electronic coherence effects play a dominant role. We consider a model problem involving the simultaneous evolution of wave packets on two coupled electronic states. We analyze the problem qualitatively from both quantum and semiclassical perspectives using perturbation theory, and identify the roles played by coupling strength and relative phase of the initial wave packets. We then perform trajectory-based simulations on a two-state one-dimensional model problem and compare the results with those of exact quantum calculations. In marked contrast with most current methods for modeling nonadiabatic dynamics with classical trajectories, the semiclassical Liouville method is found to be capable of treating even dominant electronic coherence effects in a consistent and accurate manner. © 2000 American Institute of Physics.
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