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  • 1985-1989  (13)
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Material
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Lattice theories of polymeric fluids (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 2194-2203 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100343a006
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray structural characterization of larger CdSe semiconductor clusters (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7282-7290 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: X-ray powder patterns obtained from three different types of 35–40 A(ring) CdSe nanoclusters are analyzed. We simulate the effects of thermal fluctuations, stacking faults, surface reconstructions, and bond compressions on powder patterns of CdSe clusters using the Debye formula. We find that the spectra of capped and annealed CdSe particles grown in inverse micelles are best fit by a mixture of crystalline structures intermediate between zinc-blende and wurtzite. We describe a new preparation for CdSe clusters, the structure of which appears to be well-defined wurtzite with, on average, less than one stacking fault per cluster. Thermal effects are found to be important and to mask the subtle effects of likely surface and core reconstructions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457295
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Observation and analysis of the ν3 band of NH+3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5910-5917 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν3 degenerate vibration–rotation band of the ammonia cation NH+3 was observed and analyzed. The spectrum was detected in direct absorption using a tunable difference frequency spectrometer combined with velocity modulation. The ion was produced in a 6 kHz ac discharge with a gas mixture of He:H2:NH3 (∼250:8:1) and with a total pressure of ∼6 Torr. Spin–rotation splittings for most Q-branch transitions were well resolved and spin–rotation interaction constants were determined. A symmetric rotor Hamiltonian with A1–A2 splittings and l resonance was used to analyze the spectrum. The spectral pattern indicates that NH+3 is a planar molecular with D3h symmetry, consistent with a 2A‘2 ground electronic state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456356
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Difference frequency laser spectroscopy of the ν3 fundamental band of NH+2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5918-5923 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν3 band of NH+2 in the X˜ 3B1 ground electronic state was observed in direct absorption with a tunable difference frequency laser spectrometer in the 3 μ region, using velocity modulation detection. NH+2 and NH+3 ions were generated in an ac discharge of He and NH3, or of He, N2, and H2. Fifty-three rovibrational transitions were measured and fit to a triplet A-reduced Hamiltonian to determine rotational, centrifugal distortion, and spin–rotation constants. The band origin was found to be ν0=3359.932 cm−1, in excellent agreement with a recent calculation of Jensen, Bunker, and McLean. Indirect evidence from the spectrum suggested that NH+2 is quasilinear, but selection rules prevented a determination of the A rotational constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456357
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  • 5
    Electronic Resource
    Electronic Resource
    A lattice model for self- and mutually avoiding semiflexible polymer chains (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3720-3730 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce a spin field theory for many self- and mutually avoiding polymers with arbitrary stiffness on a regular lattice. The model allows for the complete crossover between flexible polymers and rods. The model also includes arbitrary polymer length distributions and arbitrary volume fractions from the highly dilute regime to the melt. The mean field approximation to the full theory reproduces Flory theory, but our model permits a rigorous and systematic evaluation of corrections to the mean field approximation. The corrections are in the form of a double expansion in powers of the volume fraction ψ and, formally, in powers of the inverse lattice coordination number z−1. We present the correction to first order in z−1 and discuss its relevance to the entropic contribution to the Flory χ parameter for semiflexible polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451974
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  • 6
    Electronic Resource
    Electronic Resource
    Osmotic pressure of star and ring polymers in semidilute solution (1986)
    s.l. : American Chemical Society
    Macromolecules 19 (1986), S. 2770-2778 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00165a019
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  • 7
    Electronic Resource
    Electronic Resource
    Systematic corrections to Flory–Huggins theory: Polymer–solvent–void systems and binary blend–void systems (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2741-2756 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A field theory, presented earlier by us, which is formally an exact mathematical solution of the Flory–Huggins lattice model, is used to evaluate corrections to Flory–Huggins mean field theory in a systematic series expansion in the inverse of the lattice coordination number and in the nearest-neighbor interaction energies. We explicitly determine the first few corrections to the free energy of mixing for polymer–solvent–void systems and for systems containing two kinds of polymers and voids (binary blend–void systems). Applications of the theory to the calculation of equations of state and effective Flory χ parameters are discussed. We compare the result of our theory with the lattice Monte Carlo data of Dickman and Hall for the chain insertion probability and for the pressure in a system of athermal chains and voids. Good quantitative agreement is found. We discuss shortcomings of the lattice model in representing real polymers as well as possible extensions of the model to remedy these deficiencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454005
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  • 8
    Electronic Resource
    Electronic Resource
    Lattice models of polymer solutions: Monomers occupying several lattice sites (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 7272-7284 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An exact field theory is presented to describe a system of self-avoiding lattice polymer chains with arbitrary regularly branched architecture. Equivalently, the chains can be viewed as linear and as composed of structural units (monomers) having a chosen shape and size and therefore each occupying more than one lattice site. The mean field approximation coincides with Flory's theory, and it does not distinguish among chain geometries. However, we develop a systematic expansion for corrections to mean field approximation in powers of z−1 where z is the lattice coordination number. The entropy per site, the pressure and the chain insertion probability are computed for various chain architectures to O(z−2). At equal lattice site coverages per chain and total polymer volume fraction, the more compact the polymer chain geometry the higher is the insertion probability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453320
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    A lattice field theory for polymer systems with nearest-neighbor interaction energies (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 5534-5540 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We generalize a lattice field theory that formally provides an exact description of the statistical mechanical entropy of nonoverlapping flexible polymers to enable treatment of nearest-neighbor interaction energies. The theory is explicitly solved within an extended mean field approximation for a system of polymer chains and voids, and we also provide mean field results for polymer–solvent–void and binary blend–void mixtures. In addition to recovering the Flory–Huggins mean field approximation for these systems, our extended definition of the mean field approximation contains a set of corrections to Flory–Huggins theory in the form of an expansion in powers of the nearest-neighbor interaction energies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453638
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  • 10
    Electronic Resource
    Electronic Resource
    Statistical mechanics of the packing of rods on a lattice: Cluster expansion for systematic corrections to mean field (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3007-3022 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We introduce a lattice spin field theory which formally provides an exact description of the statistics of nonoverlapping, nonintersecting rods on regular lattices. The theory is applicable to arbitrary rod length distributions and arbitrary volume fractions. The mean field approximation reproduces Flory–Huggins theory for rods on a strict lattice, but our theory permits the rigorous and systematic evaluation of corrections to the mean field entropies. We present those corrections as a cluster expansion for the entropy density which involves a double expansion in powers of the volume fraction ψ and the inverse of the lattice coordination number z−1. Our results are compared for specific cases with those of DiMarzio's theory which is more accurate than mean field. For dimers which are equally distributed among the possible lattice directions of a hypercubic lattice, we find very good agreement between our theory and DiMarzio's with ours giving a slightly larger entropy density when corrections to mean field to order ψ4 are included. Through order ψ3, our entropy for longer rods is identical to that of DiMarzio's expanded similarly. Our dimer results, however, demonstrate that the ψ4 term for rods contains contributions which we attribute to locally ordered configurations and which are absent in DiMarzio's theory. Our results are compared with the exact entropy density for dimers fully covering an infinite square planar lattice; the inclusion of corrections to mean field up to order z−2 narrows the error from 33.8% for mean field to 7.85%. Our theory, however, also describes the dimer–monomer problem which has not been very amenable to analytic theories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451830
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