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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2599-2608 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Proton transfer in ammonia–nitric acid clusters containing up to four component units are subject to theoretical calculation in this work. In a single ammonium nitrate unit, proton transfer between the nitric acid and ammonia unit does not occur but the two molecules are strongly hydrogen-bonded. In a cluster of two ammonium nitrate formula units [NH3HNO3]2, proton transfer does occur and the components are stabilized by ionic interactions. Ammonium nitrate solvated with single ammonia [NH3HNO3]NH3 or nitric acid [NH3HNO3]HNO3 molecules are also studied. Structural changes in the various clusters relative to the free molecules are discussed. Using population analysis, the total electrostatic interaction between the components of each cluster are calculated. It is argued that the magnitude of the total electrostatic interactions within the cluster determines whether proton transfer and ion formation takes place. Binding energies alone do not give a reliable indication of the occurrence of proton transfer. © 2002 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1882-1890 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a theoretical framework for study of chemical dynamics induced by a scanning tunneling microscope. An analytically solvable limit of the expression derived for the reaction rate reveals the information content of the voltage dependence of the observable. The theory is applied to the problem of H-atom desorption from a silicon surface in the 4–10 V range, where desorption is triggered by a single electronic transition into a short-lived excited state localized on the H–Si bond. The resonance lifetime is extracted by fitting the numerical results to an observed desorption yield versus voltage curve [Foley et al., Phys. Rev. Lett. 80, 1336 (1998)]. © 2001 American Institute of Physics.
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical study of tip-induced desorption of benzene from a Si(100) surface is presented. The energetically forbidden process is triggered by inelastic resonance tunneling mediated by a cationic state of the substrate–adsorbate complex. Potential energy surfaces for the neutral and ionic states are computed within a cluster model. Quantum mechanical time-dependent wave packet calculations are used to explore the desorption dynamics. Extension of the scheme to study the response of different classes of organic adsorbates to tunneling current and to control of other surface reactions with a scanning tunneling microscope is discussed. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6909-6921 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new method is developed for deriving first order density corrections to gas transport coefficients using the time correlation function formalism. In a moderately dense gas, both kinetic and potential contributions to the flux are significant. This article extends the projection operator technique developed in our previous work for purely kinetic flux operators [J. Chem. Phys. 109, 3452 (1998)] to include the effects of the potential contribution to the flux. The method introduces two projection operators, one for each of the kinetic and potential flux contributions, with the consequence that the calculation of a transport coefficient involves a matrix associated with the two flux contributions, and the inversion of this matrix. The binary collision expansion of the resolvent in each of the matrix elements allows a transport coefficient at moderate gas densities to be expressed in terms of integrals over functions of the intermolecular potential. In the following article, it is shown that these results are consistent (that is, within a similar level of approximation of the integrals) with the known density corrections for the coefficients of viscosity and thermal conductivity. © 1999 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6922-6931 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An equation for a moderately dense gas transport coefficient, derived in the preceding article from time correlation function theory, is specialized to the estimation of the coefficients of viscosity and thermal conductivity. These equations include the first order in density correction to the transport coefficient, but are restricted to being valid only for repulsive potentials. It is shown that the resulting expressions are, within a series of analogous approximations, identical to those obtained by solving the generalized Boltzmann equation. © 1999 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8533-8542 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The values of gas transport coefficients, when both unbound particles and bound pairs are present, are standardly accounted for by treating the gas as a mixture of free atoms and bound pairs and using the well-known expressions for the transport coefficients for a mixture. But since the bound pairs consist of two atoms, it should also be possible to start from a purely atomic picture of the gas. This paper accomplishes that aim, starting with the time correlation function expression for the transport coefficient in terms of atomic variables. © 1999 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3452-3460 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The connection between the low density limit of the time correlation equations for the transport coefficients and the solution of the Boltzmann equation to lowest order approximation appear to have been made in essentially two different ways. Either the time correlation function is evaluated by using the time dependent (linearized) Boltzmann equation, or by utilizing a resummation of an expansion in the reciprocal of a convergence parameter. As well, the connection is often made to only the lowest order solution of the Boltzmann equation, ignoring the possible importance of higher order moments (Sonine polynomials) in the solution of the Boltzmann equation. The present work uses a projection operator method and a subsequent binary collision expansion of the time correlation function to retain all contributions to the transport coefficient from binary collisions. This explicitly avoids an expansion in a divergent parameter and reproduces all Sonine polynomial contributions to the transport coefficient. Gas transport coefficients for a binary mixture are obtained in a similar manner. © 1998 American Institute of Physics.
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  • 8
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1463-1466 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Formal collision theory indicates that the absolute termolecular recombination reaction rate can be expressed in a form associated either with direct or indirect mechanisms for the recombination. Moreover, the same exact rate constant can be calculated using either of the four mechanisms. These results are to be contrasted to the rate constants standardly calculated by approximate methods. © 1997 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 706-714 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For a closed system, the integration (trace in the quantum case) over one particle of a reduced distribution function is related to the reduced distribution function of one lower order. The particular details of this "chain" relation depend sensitively on the detailed manner in which the reduced distribution functions are defined, specifically their normalization. Correlation functions are defined in terms of reduced distribution functions, which fixes the normalization of the correlation functions and, provided they exist, their associated chain relations. Chain relations for the correlation functions are shown to exist for normalizations of generic type but not for normalizations of specific type. The normalization requirement is shown, in general, to prevent the direct association of correlation functions with physical clusters, which is commonly assumed in the literature. These relations are illustrated for an ideal gas of monomers and dimers. The effect of taking the thermodynamic limit on the chain relations for this system is discussed. This illustrates how the thermodynamic limit generally destroys the chain relations. © 1998 American Institute of Physics.
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