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  • 1990-1994  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    A quantitative approximation for the quantum dynamics of hydrogen transfer: Transition state dynamics and decay in ClHCl− (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1975-1987 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general method for studying transition state spectroscopy and dynamics in hydrogen atom transfer reactions is presented. This approach is based on the time-dependent self-consistent field (TDSCF) approximation and is applied to a study of the ClHCl− photodetachment experiments of Metz et al. [Metz et al., J. Chem. Phys. 88, 1463 (1988)]. Comparison of results of exact time-dependent and TDSCF calculations are made for collinear and three-dimensional (J=0) approximations for the quantum dynamics. When ClHCl is constrained to be collinear, the TDSCF calculation overcorrelates the motions in the H atom displacement and ClCl extension coordinates. This results in relatively poor agreement with the exact result for many properties of the wave function. In contrast, when the system is propagated in the three vibrational coordinates of the system, the transition state dynamics are effectively over much more rapidly. Consequently, the TDSCF approximation yields results of very good quantitative accuracy over the time required for most of the wave function to decay off of the transition state. Comparison is also made between the wave function that results from the exact propagation and from TDSCF when the wave function in the ClCl stretch coordinate is approximated by a Gaussian wave packet. Here the magnitude of the overlap between the two TDSCF wave functions in the H atom coordinates, for quantum and semiclassical propagations of the wave function in the ClCl distance coordinate, is greater than 0.98 over the time of the propagations. These TDSCF calculations are repeated for a wave function that is approximated by a product of a two-dimensional wave function in the hydrogen atom coordinates and a one-dimensional wave function in the ClCl extension coordinate and even better quantitative agreement with the exact propagation is achieved. The success of this method for studying ClHCl gives us confidence that TDSCF will provide a general powerful tool for studies of hydrogen and proton transfer reactions in large systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467707
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Solvation effects on association reactions in microclusters: Classical trajectory study of H+Cl(Ar)n (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 343-355 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The role of solvent effects in association reactions is studied in atom-cluster collisions. Classical trajectory studies of the systems H+Cl(Ar)n (n=1,12) are used to investigate the influence of size, structure, and internal energy of the "microsolvation'' on the H+Cl association reaction. The following effects of solvating the chlorine in an Arn cluster are found. (1) In the H+ClAr system there is a large "third body'' effect. The single solvent atom stabilizes the newly formed HCl molecule by removing some of its excess energy. The cross section found at low energies is a substantial fraction of the gas-kinetic cross section. The molecule is produced in highly excited vibrational-rotational states. (2) Some production of long-lived HCl...Ar complexes, with lifetimes of 1 ps and larger, is found for the H+ClAr collisions. Weak coupling stemming from the geometry of the cluster is the cause for long life times. These resonance states decay into HCl+Ar. (3) At low collision energy (E=10 kJ/mol) for H+Cl(Ar)12, the H+Cl association shows a sharp threshold effect with cluster temperature. For temperatures T≥45 K the cluster is liquidlike, and the reaction probability is high. For T≤40 K the cluster is solidlike, and there is no reactivity. This suggests the potential use of reactions as a signature for the meltinglike transition in clusters. (4) At high collision energies (E=100 kJ/mol) H atoms can penetrate also the solidlike Cl(Ar)12 cluster. At this energy, the solid–liquid phase change is found not to increase the reaction probability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468141
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo studies of small B(H2)n clusters (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2577-2591 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure and stability of clusters of a boron atom with one to eight H2 molecules is investigated. For the simplest BH2 clusters, the lowest ab initio adiabatic potentials for o-H2 and p-H2 interacting with a boron atom are used. For the larger clusters (n=2–8), the p-H2 is treated as a sphere, and the total potential is taken to be the sum of pairwise additive B–H2 and H2–H2 interactions which include, in the former case, an anisotropy due to the orientation of the unpaired B 2p electron. This electronic interaction is considerably more attractive when H2 approaches the B atom in a plane perpendicular to the orientation of the 2p orbital. The local and global minima on these potential surfaces were located and diffusion quantum Monte Carlo simulations were used to determine the energies and properties of the ground state wave functions for these B–(H2)n clusters. For the B(H2) cluster, a comparison is made with the results of variational calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468432
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    A perturbed-mean-field approach to the decay rates of excited vibrational states in extended systems: An application to I2(Ne)n (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4355-4366 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for calculating decay rates of vibrational modes in large polyatomic systems is proposed and tested. The high frequency excited vibration is treated quantum mechanically, and the soft modes are described classically. The initial state is described by the hybrid quantum/classical self-consistent-field (SCF) approximation. The formalism is based on a golden-rule expression. The driving potential is the difference between the full Hamiltonian and the mean field Hamiltonian (SCF) causing the decay of the initial state to final mixed quantum/classical SCF states. These states are calculated using an extension of the usual static mean-field techniques to systems with mixed quantum and classical degrees of freedom. The formalism for obtaining the mean-field states and calculating the decay rates is presented, and the method is applied to a diatomic molecule treated quantum mechanically, embedded in a 1D model for a rare gas cluster treated classically. The dependence of the eigenenergies of the quantum and the decay rates with temperature is studied. The influence on the system size is also presented and compared with the prediction of the isolated binary collision model. The effect of a change in the linear density of the cluster on the eigenenergies of the vibrational mode is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466318
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Molecule–corrugated surface collisions: Converged close coupling wave packet and quasiclassical trajectory calculations for N2 scattering from corrugated lattices (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 704-720 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The close coupling wave packet (CCWP) and quasiclassical trajectory methods are used to study rotationally inelastic scattering of N2 from static, corrugated surfaces. The collision energy in these calculations ranges from 10 to 100 meV; 18 711 quantum states are included in the highest energy calculations to ensure convergence. The scattered molecules are analyzed with respect to the polarization of the final angular momentum vector and the amount of energy transferred into rotational motion and translational motion parallel to the surface. Comparisons of quantum and quasiclassical results show that quantum effects are important even with the relatively large mass of N2 and the high scattering energies used and can be seen even after summing over many final quantum states. A test of a factorization relation derived from the coordinate-representation sudden (CRS) approximation gives qualitative agreement with the exact quantum results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465743
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Treatment of zero-point motions in cluster dynamics: Semiclassical time-dependent self-consistent-field simulation of (Ne)N (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8637-8643 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A semiclassical time-dependent self-consistent-field (TDSCF) method is developed for dealing with the difficulties caused by the nonpreservation of zero-point energy in classical molecular dynamics simulation. The method is applied to a collinear model of a (Ne)12 cluster at very low temperatures. Classically, this system dissociates rapidly due to its zero-point energy. We show that the system remains stable when treated by the new method. The normal mode dynamics of the anharmonic cluster are calculated and discussed. Interesting results are obtained on the lifetimes of single-mode states and energies due to the coupling between the modes. Some of the single-mode states have subpicosecond lifetimes, while others are stable for at least 60 ps. The results illustrate the power of semiclassical TDSCF as a tool for studying the vibrational dynamics of anharmonic cluster at very low temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465587
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    Paper (German National Licenses)
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