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  • 1
    Electronic Resource
    Electronic Resource
    An effective barrier model for describing quantum mechanical activated rate processes in condensed phases (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7342-7352 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An analytic variational model is developed to treat quantum activated rate processes in condensed phase systems. An effective parabolic barrier curvature in this model describes both the barrier nonlinearity along the reaction coordinate as well as the influence of dissipation from the fluctuating condensed phase environment. The theory is developed by exploiting the relationship between the statistics of Feynman path integral centroid densities and the rate of quantum activated events. The result is numerically tested on a model activated dynamics problem and applied to estimate the quantum tunneling correction to an SN2 reaction in water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460218
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  • 2
    Electronic Resource
    Electronic Resource
    Infrared laser-induced chaos and conformational disorder in a model polymer crystal: Melting vs ablation (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6081-6091 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics-based computer simulations are presented for the interaction of one and two infrared (IR) laser beams with a model polymer surface. When a single laser beam system is studied over a wide range of intensities, only melting of the polymer, or melting followed by bond dissociation, is observed for up to 100 picoseconds. In contrast, the two-laser simulation results exhibit a marked difference in the energy absorption behavior of the irradiated polymer which, in turn, results in multiple bond dissociations. The results for the one- and two-laser cases studied can be divided into four different classes of physical behavior: (a) the polymer remains in the solid state; (b) the polymer crystal melts; (c) the polymer ablates, but with significant melting (charring); or (d) the polymer ablates with minimal melting. Damage to the model polymer crystal from absorption of energy from either one or two lasers occurs through a mechanism that involves the competition between the absorption of energy and internal energy redistribution. The rate of energy loss from the absorption site(s) relative to the rate of absorption of energy from the radiation field determines rather the polymer melts or ablates (low absorption rates lead to melting or no change and high rates lead to ablation). A sufficiently large rate of energy absorption is only obtainable through the use of two lasers. Two lasers also significantly decrease the total laser intensity required to cause polymer crystal melting. The differences between the one- and two-laser cases are studied by adapting novel signal/subspace techniques to analyze the dynamical changes in the mode spectrum of the polymer as it melts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459496
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  • 3
    Electronic Resource
    Electronic Resource
    Rigorous formulation of quantum transition state theory and its dynamical corrections (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7749-7760 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe a procedure for computing the thermal rate constants for infrequent events that occur in complicated quantum mechanical systems. Following the ideas of Gillan, the procedure focuses on the equilibrium statistics of the centroids for the imaginary time quantum paths. We argue that the imaginary time statistics can be used to efficiently bias Monte Carlo sampling of the real time reaction dynamics. Consideration of imaginary time paths or equilibrium statistics alone leads to a quantum transition state theory. Analytical versions of this transition state theory are developed with the aid of a variational principle. Numerical applications of the quantum transition state theory are given for the one-dimensional Eckart barrier problem and for the nonseparable two-dimensional collinear H2+H reaction. Remarkably accurate results are obtained. The quantum transition state theory we describe provides a rigorous basis and generalizes algorithms recently employed to treat electron transfer and also ionization in polar media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457242
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  • 4
    Electronic Resource
    Electronic Resource
    Quasidissipative intramolecular dynamics: An adiabatically reduced coupled equations approach (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5272-5279 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quasidissipative intramolecular dynamics of experimentally prepared nonstationary states in large, isolated polyatomic molecules are examined using an adaptation of the adiabatically reduced coupled equations approach [J. Chem. Phys. 84, 2254 (1986)]. Under appropriate conditions, the present method predicts an exponential decay of the initial state probability which has a "generalized'' Golden Rule-like decay rate constant. The present dynamical approach is complementary to approximate resolvent operator techniques commonly employed in radiationless transitions theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453670
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  • 5
    Electronic Resource
    Electronic Resource
    An effective Golden Rule decay rate expression for quasidissipative IVR processes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5547-5552 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An effective Golden Rule rate expression is derived for the intramolecular vibrational decay dynamics of an initially prepared nonstationary state in an isolated polyatomic molecule. It is shown that the decay rate of the initial state depends on the properties of those states which are directly coupled to the initial state. In many cases, there may be a suppression of the exponential decay rate. An explanation for the insensitivity of some experimental C–H overtone linewidths with increasing excitation energy is also proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454754
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  • 6
    Electronic Resource
    Electronic Resource
    Iteratively determined effective Hamiltonians for the adiabatically reduced coupled equations approach to intramolecular dynamics calculations (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5019-5026 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An iterative procedure is proposed for determining increasingly accurate effective Hamiltonians for use in the adiabatically reduced coupled equations approach to intramolecular dynamics calculations [J. Chem. Phys. 84, 2254 (1986)]. The relationships between this iterative determination of the effective Hamiltonian, which is based on an adiabatic approximation, and some other partitioning methods for determining an effective Hamiltonian are discussed. The present iterative procedure provides accurate agreement with the exact dynamics for the two specific model systems studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451691
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  • 7
    Electronic Resource
    Electronic Resource
    Ab initio molecular dynamics simulation of the Ag(111)-water interface (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7196-7206 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of a first-principles study of the structure of the Ag(111)–water interface are presented. The calculations were carried out using an ab initio Car–Parrinello molecular dynamics simulation within a pseudopotential formalism and the generalized gradient approximation to the exchange-correlation potential. Periodic five layer slabs covered with 48 water molecules were employed to simulate the structure of the interface. An analysis of the structural properties of the interface shows that the preferable places of residence of H2O molecules in the contact overlayer are the metal top sites. The electronic structure of the interface has also been explored. It was found that there is a strong coupling of the water overlayer with the metal crystal electronic states. However, the surface-state charge density is only slightly disturbed by the presence of water. The empty surface states are seen to not be quenched by the presence of water, which is in qualitative agreement with existing experiments. The electrons donated to the metal by the water fill the metal crystal electronic states, which is responsible for the dominant coupling of the metal with the water system. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1403438
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio molecular dynamics simulation of the Cu(110)–water interface (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3248-3257 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of a first principles simulation of the Cu(110)–water interface are presented. The calculations were carried out using ab initio Car–Parrinello molecular dynamics simulation within a pseudopotential formalism and the BLYP generalized gradient approximation to the exchange-correlation potential. An analysis of the structural properties of the interface shows that absorption of H2O molecules occurs on the metal top sites which is in agreement with experimental results. The electronic structure of the interface has also been explored. It was found that there is a strong coupling of the water overlayer with the metal crystal electronic states. However, the surface-states charge density is undisturbed by the presence of water. The empty surface states are seen to not be quenched by the presence of water, which is also in qualitative agreement with existing experiments. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1342859
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  • 9
    Electronic Resource
    Electronic Resource
    Modeling the free energy surfaces of electron transfer in condensed phases (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 5413-5424 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a three-parameter model of electron transfer (ET) in condensed phases based on the Hamiltonian of a two-state solute linearly coupled to a harmonic, classical solvent mode with different force constants in the initial and final states (a classical limit of the quantum Kubo–Toyozawa model). The exact analytical solution for the ET free energy surfaces demonstrates the following features: (i) the range of ET reaction coordinates is limited by a one-sided fluctuation band, (ii) the ET free energies are infinite outside the band, and (iii) the free energy surfaces are parabolic close to their minima and linear far from the minima positions. The model provides an analytical framework to map physical phenomena conflicting with the Marcus–Hush two-parameter model of ET. Nonlinear solvation, ET in polarizable charge-transfer complexes, and configurational flexibility of donor-acceptor complexes are successfully mapped onto the model. The present theory leads to a significant modification of the energy gap law for ET reactions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289886
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  • 10
    Electronic Resource
    Electronic Resource
    Semiclassical theory of Fermi resonance between stretching and bending modes in polyatomic molecules (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4064-4072 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Approximate semiclassical solutions are developed for a system of a Morse oscillator coupled to a harmonic oscillator via a nonlinear perturbation. This system serves as a model for the interaction of an excited stretching mode with a bending mode in a polyatomic molecule. Three semiclassical methods are used to treat this model. In particular, a matrix diagonalization, a two-state model, and a uniform semiclassical approximation (USC) based on Mathieu functions are each used to determine the splittings and state mixing involved in these stretch–bend Fermi resonances. For small perturbations, approximate analytic semiclassical expressions are obtained for the system treated. These analytic expressions are given for the splittings using a two-state or USC method and for the overlaps of the zeroth order states with the eigenstates of the molecule using a USC method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448847
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