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  • 1
    Electronic Resource
    Electronic Resource
    Modeling orientational randomization in zeolites: A new probe of intracage mobility, diffusion and cation disorder (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2893-2905 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed kinetic Monte Carlo simulations of benzene orientational randomization (BOR) and diffusion in Na-Y zeolite for various Na(II) occupancies and Na(II) spatial patterns. Full Na(II) occupancy gives BOR rates controlled by intracage motion, whereas half Na(II) occupancy gives BOR rates sensitive to both intracage and intercage motion, but insensitive to particular Na(II) spatial patterns. Alternatively, BOR with one quarter Na(II) occupancy demonstrates qualitative sensitivity to different Na(II) spatial patterns. Calculated diffusion coefficients vary weakly with decreasing Na(II) occupancy until ca. one Na(II) per supercage. Diffusion coefficients and mean square displacements reveal no information about intracage motion, and are insensitive to different spatial patterns of Na(II) cations. Our computational results thus suggest that measuring orientational randomization in zeolites can provide important information regarding intracage motion, diffusion and cation disorder. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473352
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  • 2
    Electronic Resource
    Electronic Resource
    Analytical theory of benzene diffusion in Na-Y zeolite (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 7810-7815 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have developed an analytical expression for the diffusion coefficient of benzene in Na-Y at infinite dilution in terms of fundamental rate coefficients, which has been confirmed by extensive kinetic Monte Carlo simulations. This model assumes that benzene jumps among SII and W binding sites, located near Na+ ions in 6-rings and in 12-ring windows, respectively. Our diffusion theory is based on D=〈fraction SHAPE="CASE"〉16ka2 where a≅11 Å is the intercage length and k is the cage-to-cage rate coefficient. We have determined that k=k(SII→W)⋅〈fraction SHAPE="CASE"〉12⋅3[1+k(W→W)/k(W→SII)], a finding that has resolved discrepancies between theory and simulation and has suggested new interpretations of benzene diffusion in Na-Y. When α(T)≡k(W→W)/k(W→SII) is between 0 and 1, the factor 3[1+α(T)] counts the number of thermally allowed target sites for cage-to-cage motion. Alternatively, when α(T)(very-much-greater-than)1, benzene mobility is interpreted as interstitial diffusion, wherein k is controlled by the probability of W site occupancy multiplied by the rate of W→W jump processes. This limit is expected to arise with benzene loadings of four molecules per supercage. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473738
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  • 3
    Electronic Resource
    Electronic Resource
    Transport Theory for Cationic Zeolites: Diffusion of Benzene in Na-Y (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 10600-10608 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100026a025
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  • 4
    Electronic Resource
    Electronic Resource
    Efficient polynomial expansion of the scattering Green's function: Application to the D+H2(v=1) rate constant (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1103-1112 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply the absorbing boundary condition (ABC) discrete variable representation (DVR) theory of quantum reactive scattering to the initial state selected D+H2(v=1, j)→DH+H reaction. The ABC-DVR Green's function is efficiently computed by a Newton polynomial expansion. We compute accurate reaction probabilities for the total energies and angular momenta required to obtain the thermal rate constants kv=1, j(T). At T=310 K, a thermal average over j=(0,1,2,3) is performed to yield the final result kv=1(310 K)=1.87×10−13 cm3 molecule−1 s−1, in quantitative agreement with the most recent experimental value (1.9±0.2)×10−13 cm3 molecule−1 s−1. The J-shifting approximation using accurate J=0 reaction probabilities is tested against the exact results. It reliably predicts kv=1(T) for temperatures up to 700 K, but individual (v=1, j) selected rate constants are in error by as much as 41%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466642
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum mechanical reaction probabilities with a power series Green's function (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6917-6928 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new method to compute the energy Green's function with absorbing boundary conditions for use in the calculation of quantum mechanical reaction probabilities. This is an iterative technique to compute the inverse of a complex matrix which is based on Fourier transforming time-dependent dynamics. The Hamiltonian is evaluated in a sinc-function based discrete variable representation, which we argue may often be superior to the fast Fourier transform method for reactive scattering. We apply the resulting power series Green's function to the calculation of the cumulative reaction probability for the benchmark collinear H+H2 system over the energy range 0.37–1.27 eV. The convergence of the power series is found to be stable at all energies and accelerated by the use of a stronger absorbing potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464759
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  • 6
    Electronic Resource
    Electronic Resource
    Diffusion in zeolites via cage-to-cage kinetics: Modeling benzene diffusion in Na-Y (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 3753-3760 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed kinetic Monte Carlo simulations of benzene diffusion in Na-Y (Si:Al=2.0) over the temperature range 200–500 K. For hopping on a tetrahedral lattice, we derive the analytical formula for D in terms of hopping lengths and times, yielding the simple-cubic relation D=1/6ka2, even though the lattice is very different from simple cubic. We have calculated the distribution of cage residence times for benzene in Na-Y, finding single exponential decay controlled by the SII→W rate coefficient, even though several processes contribute to intercage motion. Exact agreement between mean square displacement slopes and 1/6ka2 is obtained only when using kinetic intercage hopping lengths, which are found to be in excess of the static length by as much as 0.54 A(ring). Constructing diffusion coefficients from intercage lengths and times provides overwhelming computational speedups over calculating mean square displacements. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472195
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  • 7
    Electronic Resource
    Electronic Resource
    Teaching Materials that Matter: An Interactive, Multi-media Module on Zeolites in General Chemistry (1999)
    Springer
    The chemical educator 4 (1999), S. 114-118 
    Details
    ISSN: 1430-4171
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper describes a two-week teaching module, based on the structure, properties, and applications of zeolites, that was taught in a general chemistry course. We chose to focus this module on zeolite science because of the beauty and versatility of zeolites as well as their many existing and potential uses in the chemical industry. The curriculum was centered around an interactive educational computer program about zeolites that we developed specifically for the module, entitled “Zeolite Explorer.” The module also involved class lectures by faculty, a guest lecture from an industry leader, homework problems, handouts, overheads, and demonstrations. The class outline, lecture notes, handouts, overheads, homework, and “Zeolite Explorer” software are included with this article. We believe that this interactive, multimedia approach to teaching zeolite science generated more student interest in chemistry and learning an extremely important subject.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00897990300a
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