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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an approximate quantal model to study the double continuum problem arising in the complete fragmentation of X⋅⋅⋅BC(v)⋅⋅⋅Y van der Waals(vdW) complexes, where BC is a conventional diatomic molecule vibrationally excited and X and Y are rare gas atoms, through vibrational predissociation (VP). Assuming a near equilibrium geometry of the complex and using an adiabatic approximation for describing the oscillation in the angle formed by the BC⋅⋅⋅X and BC⋅⋅⋅Y weak bonds, the rates for complete fragmentation are expressed in the frame of Fermi's "Golden Rule''. Double continuum wave functions may be obtained by a perturbative treatment that allows one to take properly into account the symmetry of the problem in the particular and very frequent case X≡Y.
    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 87 (1987), S. 1054-1061 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an adiabatic angular approximation, closely related to the infinite order sudden approximation, to treat rotational predissociation of triatomic van der Waals complexes formed by a rare gas atom and a diatomic molecule that is treated as a rigid rotor. The metastable states of the complex are obtained as discrete solutions of the Schrödinger equation while the corresponding continuum solutions allow us to estimate the rates for rotational predissociation, within the framework of the Golden Rule approximation, after the relevant discrete-continuum dynamical couplings are calculated. Applications to the He–CO, He–N2, and He–O2 systems are presented.
    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 94 (1991), S. 4230-4233 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time-dependent wave packet technique is applied to the Golden Rule treatment of vibrational predissociation. The wave packet at time zero is taken as the product of the quasibound wave function and the coupling inducing predissociation. The rate for vibrational predissociation can then be obtained by Fourier transform into the energy domain of the time-dependent wave packet autocorrelation function. The method has been applied to a model triatomic van der Waals molecule. It is shown that when the bound-state components of the wave packet are projected out, the time-dependent version of the Golden Rule approximation provides an alternative efficient technique to treat intramolecular decay.
    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 94 (1991), S. 7868-7874 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of vibrational predissociation (VP) of van der Waals (vdW) I2⋅⋅⋅Nen clusters is studied by means of a quasiclassical trajectory approach. We assume a near-equilibrium geometry that accounts for the I2 stretch and the stretching and bending modes of the rare gas atoms restricted to move along a plane perpendicular to the I2 axis. A sharp increase of the halfwidth is observed for n=9 together with certain stability of the n=8 cluster size with respect to dissociation. It would indicate the existence of a first coordination shell for Ne around I2 containing eight atoms. In addition, the dissociation results less and less efficient as n increases and statistical mechanisms become important for the cluster sizes studied.
    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 92 (1990), S. 3348-3358 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Converged three-dimensional quantum mechanical calculations for photofragmentation of the Ne⋅⋅ICl van der Waals molecule in the energy region of the electronically excited B(3∏0+) state of ICl are presented and compared with experiments. Lifetimes and final state distributions for the ICl fragments were determined for vibrational predissociation from the lowest van der Waals level in the B(v'=2) channel. Good agreement between theory and experiment was achieved using a sum of atom–atom pairwise potentials. This potential energy surface predicts the equilibrium geometry of the complex to be bent at 140° with the Ne atom towards the Cl end of ICl. The diabatic vibrational golden rule (DVGR) approximation, as well as the rotational infinite order sudden approximation (RIOSA), have been tested again the full 3D calculations. Analysis of the quasibound wave function reveals that the highly inverted rotational distribution of the ICl fragments observed in the experiment, is not due to zero-point bending motion. It is more likely to be due to a rotational rainbow effect enhanced by the favorable initial geometry of the complex. The effect of the excitation of the bending van der Waals mode in the complex has also been studied. As compared with the lowest level, a longer lifetime and a different rotational distribution of the fragments is predicted. The results presented in this work not only elucidates many dynamical aspects of vibrational predissociation for the Ne⋅⋅⋅ICl complex, but also provide benchmark data for the study of other theoretical methods and approximations.
    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 92 (1990), S. 496-507 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of tetra-atomic X ⋅⋅⋅ I2 ⋅⋅⋅ Y van der Waals (vdW) clusters, where X,Y=He,Ne, is studied using an approximate quantal treatment. In this model the above complexes are treated as like diatomic molecules with the rare-gas atoms playing the role of electrons in conventional diatomics. Then a H2-like molecular-orbital formalism is applied, choosing the discrete states of triatomic systems I2 ⋅⋅⋅ X(Y) as molecular orbitals. Calculations at fixed configurations as well as including vdW bending motions restricted to the plane perpendicular to the I2 axis have been carried out for the sake of comparison with previous results. Finally, the restrictions are relaxed and the vdW bending motions are incorporated in a full way within the framework of a configuration interaction. The structure of these clusters is also studied through the probability density function.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6504-6513 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energetics and dynamics of van der Waals (vdW) I2⋅⋅⋅Hen clusters are studied in an approximate way by using a model that considers 2n+1 degrees of freedom, that is, the I2 stretch and the 2n stretching and bending modes of the He atoms restricted to move along a plane perpendicular to the I2 axis. For n=2,3 a configuration-interaction treatment is carried out to obtain energy levels. For n=4–8, ground-level energies are estimated from those corresponding to n=2,3 and the geometric relationships among the n vdW bonds. A quasiclassical trajectory approach is used to study the dynamics of these clusters, and lifetimes and half-widths for vibrational predissociation have been calculated for n=1–9. A large increase in the half-width of n=9 with respect to the cases n=1–8 is observed, which would imply the existence of a first coordination shell for He about I2 containing eight atoms. Also, it is found that the mechanisms of dissociation for these clusters become statistical as the number of vdW bonds increases.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic-to-vibrational energy transfer has been studied by solving numerically the close-coupling equations, in the T-shape configuration, on the two lowest electronic states of the Na–N2 system. The diabatic potential surfaces were taken from Archirel and Habitz while the interelectronic coupling was modeled by different Gaussian-type functions. Different sets of parameters for the coupling were used in order to study the final vibrational distributions of N2. Finally, partial quenching probabilities are presented and compared with previous theoretical and experimental works.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two different formalisms, one based on close-coupling equations and other on the distorted wave approximation, have been applied to the low energy elastic scattering of 4He atoms by a corrugated copper surface, Cu(110). Diffraction intensities and energetic positions and half-widths (selective adsorption resonances) have been obtained and compared with experimental and previous theoretical results, respectively. For this trapping process, and within the close-coupling framework, a plot of the diffraction channels (open and closed) has turned out to be very useful and a good guide in order to know the disposition of them at each interesting angular region. Also, a very accurate method, already employed successfully to treat resonances in the vibrational and/or rotational predissociation of van der Waals molecules, has been found to be also adequate here.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Computer Physics Communications 51 (1988), S. 207-216 
    ISSN: 0010-4655
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Computer Science , Physics
    Type of Medium: Electronic Resource
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