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  • 1970-1974  (590)
  • 1920-1924
  • 1970  (590)
  • Physics  (526)
  • Atomic, Molecular and Optical Physics  (64)
Materialart
Erscheinungszeitraum
  • 1970-1974  (590)
  • 1920-1924
Jahr
  • 1
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 97-107 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 431-450 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A one-centre CI wave function for HeH+ reported by Stuart and Matsen for 0.1 ≤ R ≤ 5.0 has been analysed in detail from the viewpoint of molecular formation. Further, by means of a natural orbital analysis, it was possible to obtain some measure of the electron correlation contained within such wave functions for various R values. These effects were illustrated by means of a series of difference maps for the electron density. One- and two-particle expectation values were obtained as a function of R. Thus, it was possible to study several aspects of the influence of the proton on the electron charge cloud as we pass from He through to the united atom Li+. The occupation numbers within the natural expansions were compared with those which arise from a similar analysis of a two-centre wave function for HeH+. The “character” of such wave functions for HeH+, and also for He and Li+, were analysed and compared.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 465-486 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The quadrupolar and octupolar distortion of the ions in the He-sequence caused by an external electro-magnetic field has been studied by a variation-perturbation method in the Hartree-Fock scheme. For certain frequencies singularities appear in the response of the system to the perturbation. Approximate representations for the excited d and f states have been obtained from a study of these resonances. Such a perturbation calculation has the advantage that representations of the different excited states are obtained independently. The orthogonality to all the lower lying levels of the same symmetry is not required. The only source of inaccuracy implicit in the procedure lies in the improper consideration of the inter-electronic interaction. This is corrected for by an independent calculation, which is again formulated in terms of a perturbation treatment. The resulting wave functions for the excited states are accurate in the Hartree-Fock model. Expectation values of several operators have been calculated with these corrected wave functions.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 365-387 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The utility of the separated electron pair (SEP) model (strongly orthogonal geminals) is examined quantitatively, for pyramidal and planar nuclear configurations of the NH3 molecule. The best SEP wave function computed for each species is capable of recovering about half of the correlation energy obtained by a fairly accurate configuration interaction (CI) calculation, (corresponding to roughly 25% of the total molecular correlation energy). It is illustrated that the model can be systematically extended with only a modest effort to yield more accurate results (about 40% of the total correlation energy). The fact that the corrections to the SEP model have a simple physical interpretation suggests that this model may be a useful starting point for “brute force” CI calculations on larger chemical systems.
    Zusätzliches Material: 23 Tab.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970) 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 451-452 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 503-518 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ab initio calculations using a small Gaussian basis set, including 3d orbitals on the sulphur atom, have been performed on the fluorosulphate radical and the related ions SO3F+ and SO3F-. A new SCF procedure is described and applied to the open shell cases discussed here. The results are compared with recent CNDO calculations and with the experimental transition energies of the radical.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 519-527 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Polikanov's perturbation method for the solution of the radial Schrödinger equation is shown to be equivalent to the usual Rayleigh-Schrödinger method but with full normalization instead of intermediate noralization. The energy corrections are shown to be the same to all orders. The computational advantages of Polikanov's method are discussed. The method is illustrated by considering the two-electron ions in the Hartree-Fock approximation.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 533-539 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A mathematical model of a molecule is proposed. The electronic structure is described using a molecular orbital wave function constructed from a small number of spherical Gaussians with optimized parameters. The models exhibit the desirable properties of numerical stability, objectivity and transferability. Results are given for CH4, C2H6, cyclo-propane, H2O, CH2O and C2H4. They can be given a chemical interpretation in terms of chemical bonds, lone pairs and atomic cusps.
    Zusätzliches Material: 6 Tab.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 1-3 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A perturbation variation treatment of two-electron atoms using exp (-αr〈 - βr〉) as the zeroth order wave function is presented. The parameters α and β are variationally determined and the results are compared with the “physical” choice α = Z, β = Z - 1, and with Z-1 theory. The energy is given through fifth order in the perturbation.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 529-532 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The systems C2H4F+ and C2H4CH3+ have been investigated by the SCF-MO-P (LCGO) method. It will be shown that the results agree with the empirical rule of Markownikoff. An explanation of the rule of Markownikoff is given by means of the computed results.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970) 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 579-586 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A detailed study of the performance of the Morse, the Hulburt--Hirschfelder and the Lippincott potential energy functions has been carried out by comparing them with the Rydberg-Klein-Rees potential energy curves for a number of electronic states of various diatomic molecules. Further, by employing the above potential energy functions, the radial Schrödinger equation has been solved for the vibrational energy levels, G(v), and the vibrational wave functions, ψv. The latter have been employed to determine the rotational constants, Bv, for the individual vibrational energy levels. Then the molecular constants, we, wexe, weye, Be, αe and γe for the various electronic states, have been computed by using the values of G(v) and Bv. A comparison of the molecular constants derived in this manner with the experimental ones reveals better agreement, in most cases, than that reported by previous workers.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970) 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 15
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The method of the MC-LCAO-MO approach, described in the preceding paper, is further applied to the benzene cation. Through the iteration process the π-electron energies and the molecular shapes are computed for the ground and two lowest excited states of the cation in both D6h and D2h geometries. A remarkable fact obtained is that a comparatively small variation of the geometrical structure (c. 0.010 - 0.013 Å bond length difference) brings about a considerable change of the energy value (c. 0.85 - 1.25 eV).The π-electronic excitation energies obtained from the iteration process are compared with the transition energies calculated from the usual method in which the structures of the excited states are assumed to be the same as the corresponding ground state structures. The difference in the excitation energy between the cation and the anion, and the CI effect on the excited states, are discussed. It is found that the doubly excited configurations play an important role in CI, which is somewhat different from that of the singly excited configurations. The stabilization energy due to the Jahn-Teller distortion is estimated for the ground state of the cation.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 149-172 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: It is the aim of the present paper to give a mathematically oriented foundation of BW-perturbation theory, which is along the lines of Kato's previous work for RS-perturbation theory. For this purpose we firstly derive the expressions of BW-perturbation theory by the use of the contour integral method (Kap. I). In Kap. II sufficient criteria for the convergence of BW-perturbation theory are derived and applied to the 1/Z-expansion of the isoelectronic series of the He atom. The characteristic differences of the derivation and convergence properties of the two different kinds of perturbation theory are discussed in detail.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 219-221 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 18
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A method for solving the Hartree-Fock problem in a finite basis set is derived, which permits each orbital to be expanded in a different basis. If the basis set for each orbital φi contains the basis functions for the preceding orbitals, φi-1, φi-2,… φ1, then the φi form an orthonormal set. One advantage over the standard Hartree-Fock method is that a different long range behavior for each orbital, as for example is required in the Hartree-Fock-Slater method, can be forced. A calculation on the ground state of beryllium is performed using the nested procedure. Very little energy is lost because of nesting, and the node in the 1s orbital disappears.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 389-395 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A group-theoretical method is presented whereby the number and identity of the non-zero components of a property tensor in a (molecular or crystalline) environment of low symmetry may be determined.
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 427-429 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The analytical conditions are obtained and discussed under which the vibronic equations for dimers can be decoupled.
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  • 21
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An upper bound for E0, which has been derived from the conjugate eigenvalue problem by Hall, is discussed. It is emphasized that the bound is only guaranteed when V is negative-definite. An alternative bound is presented which is free from this restriction, and the underlying iterative procedure is given. Hall's result is generalized to admit internuclear distances, and the theory is illustrated by a one-dimensional system with delta-function potentials. Some disadvantages of the approach are mentioned.
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  • 22
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 625-630 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Extended Gaussian orbital basis set calculations have been carried out on an assumed staggered and eclipsed classical geometrical configuration of C2H5+. The best total energies obtained for these geometries were -78.170692 a.u. and -78.170674 a.u. respectively, corresponding to a barrier to internal rotation of 1.8 × 10-5 a.u. or 11 kcal/mole. An analysis of the charge density matrix indicates that charge is distributed in these molecules in a manner consistent with the concept of hyperconjugation.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 631-631 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 57-72 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The polarization of closed shells in an alternant radical due to the field of its unpaired electron is discussed. It is shown that the Hartree-Fock solution is unstable relative to a small perturbation caused by polarization of closed shells in a long polyene radical. Its ground state is found to be antiferromagnetic with a forbidden zone in the spectra of one-particle excitations.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 73-87 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electronic structure of the benzyl radical in its ground state has been computed using a model Hamiltonian due to Pariser-Parr with full configuration interaction as well as with different truncated configurational sets built on SCF open-shell orbitals. The correlation energy corresponding to this model was found to be equal to -0.929722 eV. With the singly excited configurations only 18% of this energy is taken into account. By extending the basis to include the doubly excited configurations one can account for 94% of the correlation energy. An analysis of the accuracy of the proton hyperfine splitting calculation caused by inaccurate computation of the wave function is given. If only singly and even doubly excited configurations are taken into account one cannot hope to obtain splittings with an accuracy of more than 0.5 g. Inclusion of triply excited configurations lowers this error by one order. In addition, the use of the simple McConnell relation may lead to an error in splitting calculations of no less than 1.5 g.
    Zusätzliches Material: 9 Tab.
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  • 26
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 89-95 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Self-consistent perturbation theory is introduced to facilitate making small, simultaneous variations in orbital exponents. This is accomplished by interpreting these variations as perturbations on the quantum mechanical system. The minimum-energy condition yields a set of linear equations for the desired exponential corrections.
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  • 27
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 121-121 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 173-189 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Further energies for types of N2O4 valence structures (or valence formulae) are reported. The results indicate that two sets of formulae might give satisfactory distributions of the mobile σ-electrons. These are (i)Resonance between covalent and ionic formulae ((B) and (D) of Part II[8]);(ii)A non-paired spatial orbital formula ((F) of Part II [8]).One estimate of the σ-bond order for the NN bond is 0.4-0.5. For this, (i) is to be preferred, because it involves a much lower energy than (ii). But should the order be about 0.7, the energies of (i) and (ii) are similar, and both descriptions are satisfactory.The ionic formula of (i) involves non-localized bonding for the NO2+ moiety. It may be replaced by a formula with localized bonds, and an almost identical energy.
    Zusätzliches Material: 1 Ill.
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  • 29
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 257-270 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The problem of upper and lower bounds to the first few eigenvalues of a very large or infinite tridiagonal matrix H is studied. Those eigenvalues of a comparison-matrix Mn which are lower than a characteristic limit, together with the corresponding eigenvalues of the variational matrix Hn are shown to bracket exact eigenvalues of H. Mn differs from Hn only in the last off-diagonal element and is easily obtained from H. Sufficient conditions for lower bounds are based on a low estimate of the characteristic limit. For increasing dimensions n, the lower bounds approach the exact eigenvalues from below. As a numerical illustration, brackets to the known eigenvalues of the harmonic oscillator with a linear perturbation are calculated.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 30
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 271-287 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using the criterion for maximizing the projection of localized bond orbitals onto the space spanned by the occupied MO's, a method for constructing hybrid orbitals of a molecule is described. For illustration purposes the method is applied to single-determinant closed shell wave functions, calculated by means of ab initio and semiempirical procedures, for the molecules of methane, acetylene, ethylene, ethane, propylene, butadiene, ammonia and hydrogen cyanide. The predictions of hybridization are briefly discussed.
    Zusätzliches Material: 6 Tab.
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  • 31
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 347-353 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The charge on each atom of some ethers and chloro-substituted ethers, their dipole moments and the quadrupole coupling constants of the chloroethers have been calculated with the method suggested by Del Re. There appears to be an intimate connection between the charge density on the oxygen atoms and the capacity of forming hydrogen bond.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 32
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 5-20 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this paper the minimum principle proposed for atomic systems by Hall, Hyslop and Rees [1] is generalized to molecules. It is shown that this generalization retains the advantage of admitting the use of a larger class of trial wave functions, for example those with discontinuities, than is possible in the usual minimum energy principle. The further advantage that the upper bounds obtained by this treatment are always at least as good as those of the Rayleigh-Ritz method is also preserved.The theory is applied to the H2+ ion, potential energy curves are obtained for various “cut-off” wave functions, and the equilibrium internuclear distance is calculated. The optimization of the “cut-off” region so that the upper bound is minimized is also discussed.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 33
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 413-425 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Fifth-rank molecular polarization tensors are discussed in terms of their tensor group which includes both the spatial symmetry and the permutation symmetry of the suffixes. This latter may be described by certain four-dimensional point groups, which in the nontotally symmetric cases may be projected into three-dimensional space. The study leads to a determination of the number of independent components of these tensors and a discussion of the types of phenomena which they may be expected to produce.
    Zusätzliches Material: 1 Ill.
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  • 34
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 541-543 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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  • 35
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The Z-expansion of two-electron systems is analyzed with the Padé technique with emphasis on establishing analytical properties of the function E(Z) formally associated with the power series expansion. The concept of critical point in this connection is stressed. For this sequence it occurs at Zc = 0.911246 with E(Zc) = -0.415184. The structure of E(Z) for Z 〈 Zc is investigated.The use of Padé approximants to extrapolate values of electron affinities is emphasized.
    Zusätzliches Material: 1 Ill.
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  • 36
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 613-623 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The Schrödinger equation for helium is written as a generalized eigenvalue equation and this is solved perturbatively for the ground state. The zero order equation is taken to be that of a “six-dimensional hydrogen atom” since, in generalized eigenvalue form, this has a discrete spectrum. Although the zero-order wave function is very poor and gives only 86% of the energy the perturbation procedure is able to improve this to 99% through third-order.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 37
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 38
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 289-295 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The Hartree-Fock equations are derived in the MO-LCAO approximation for the case when the integrals (except overlap integrals) over the atomic orbitals are charge-dependent. It is shown that inclusion of the overlap matrix in the iterative procedure gives equations which are too complicated for the simple model under consideration. The approach is applied to the VESCF method in the PPP scheme.
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  • 39
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 337-339 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 40
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970) 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 41
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A multi-configuration LCAO-MO approach using a π-bond order-bond length linear relation is introduced to predict the geometrical structures for the electronic ground and excited states of unsaturated hydrocarbons. The procedure is designed to include configuration interaction in each iterative computation where the π-electron approximation is employed under the Pariser-Parr type semi-empirical treatment.The π-bond order-bond length relation is determined as rpq = 1.523 - 0.193Ppq, when the bond lengths of ethylene, benzene and naphthalene are used and the groundstate functions including the singly and doubly excited configurations are taken into account to obtain the bond orders Ppq.The iterative calculation is applied to the ground state and the two lowest excited states of the benzene anion in both D6h and D2h molecular geometries. The geometrical structures and the π-electron energies are computed for the ground and excited states of the anion; for the latter, two types of configuration species are used. It is found that the first lowest excited state is not subjected to the Jahn-Teller effect and the calculated excited state energies do not agree with the observed values (c. 1.0 ∼ 2.5 eV higher than the observed values). The latter point is discussed in detail. It is also found that the resultant ground state energy depression due to configuration mixing is not very large and the two types of configuration species used give different CI effects on the energy levels of the two lowest excited states of the anion.Finally, the stabilization energy due to the Jahn-Teller distortion is estimated for the ground state of the anion.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 42
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 333-335 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The extended method of calculation has been applied to calculate the inter-level differences of the shell of 3d-electrons in the iron group atomic system. The hydrogen-like radial orbitals have been used. The results are compared with those obtained by ordinary methods of calculation as well as with experimental data.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 43
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 355-363 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A method for the approximate calculation of matrix elements with respect to projected Hartree-Fock wave functions is proposed. The method is tested on some calculations in the many-parameter AMO method. It is found that the approximation reduces the amount of work, involved in the evaluation of the energy, by a factor of five and that it reproduces the exact values to within a few per cent.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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  • 44
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 397-411 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We describe the correlation diagram of a linear crystal, in the traditional framework of the vibronic coupling. All lattice normal modes, except the symmetrical mode, are coupled to the excitation transfer. We therefore propose an iterative method, where every mode “sees” an effective coupling arising from the interaction of the other modes with the electronic excitation. This method is applied to a simple case (the pentamer) and the results are compared with the exact solution. In the weak coupling case this procedure gives the vibronic band structure and in the strong coupling case, the electronic band accompanied by vibrational excitations. These results show that the method employed represents an interpolation approach.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 45
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 487-501 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Wave functions expressed as antisymmetrized products of strongly orthogonal geminals have been evaluated for H2O, NH3 and CH4. The geminals have been expressed as linear combinations of 2 × 2 detors constructed with localized SCF-MO's. Several ground state observables have been computed together with the electric polarizabilities and magnetic susceptibilities. In addition, a configuration interaction calculation limited to all possible double group excitations has been carried out.
    Zusätzliches Material: 1 Ill.
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  • 46
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 545-559 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Successive partitioning technique, when based on a modified bordering method for solving a system of linear equations and a relation for the inverse of a partitioned matrix leads to Feenberg's perturbation theory. This sheds light on the properties of the expansion, its bracketing properties and the nature of the “counting operators” used sometimes in this connection.
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  • 47
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 603-612 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The Li2 molecule is treated both with the method of moments and with the method of energy variation for the following distances of the nuclei R = 2aH, 4aH, 6aH, 8aH and 10aH. The calculations have been performed with the Hartree-Fock method (HF) and with the method of pseudo-potentials (PSP). The results show that the HF method and PSP method lead practically to the same result. This may be important in the treatment of more complicated molecules.
    Zusätzliches Material: 1 Ill.
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  • 48
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 123-124 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 49
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970) 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 50
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 139-147 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In an earlier paper (Bibliography [1]) it has been shown that approximate representations of excited states of atoms can be obtained from the study of the singularities in the dynamic polarizability. Starting with these wave functions a more accurate calculation of the excited states in the Hartree-Fock scheme can be made by a perturbation treatment. The resulting wave functions yield significantly improved energy values. The 21P, 31P and 41P states of the He sequence up to C4+ are studied. The expectation values of a number of operators are calculated. The results obtained by the present method compare favourably with other elaborate calculations.
    Zusätzliches Material: 4 Tab.
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  • 51
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 52
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 203-215 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ab initio molecular orbital calculations of the electronic structure of the sulphate ion have been performed in which three Gaussian-type functions are used to simulate each member of a minimal basis of Slater-type orbitals. Comparative calculations on H2S show that such a basis excellently reproduces the properties of the valence electrons given by calculations in a Slater basis. The expansion of the basis by the addition of sulphur 3d orbitals results in a large decrease in the molecular energy (1 a.u.) and has a pronounced effect on the ordering and energy of the molecular orbitals. The results of a number of semiempirical schemes are discussed in the light of these results.
    Zusätzliches Material: 7 Tab.
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  • 53
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 297-313 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A practical method for finding multi-configurational SCF wave functions is proposed. The basic equation is equivalent to the Brillouin theorem; comparison with the usual SCF equations obtained through effective hamiltonians gives an interpretation of the offdiagonal Lagrange multipliers. Numerical applications to Formaldehyde in a minimum Slater-type orbital basis with four different variational wave functions are reported. The molecular orbitals found in these calculations are localized on the chemical bonds. The largest contributions to the energy are obtained from π-π and dispersion-type σ-π correlation.
    Zusätzliches Material: 7 Tab.
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  • 54
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 341-341 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 55
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 341-342 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 56
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 223-243 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A large configuration-interaction calculation has been performed to determine the wave function, energy, and molecular properties of CO. The most important configurations were used to obtain the natural geminals and their occupation numbers. A pair-energy approach to the correlation energy was attempted with results which differ significantly from the configuration-interaction results.
    Zusätzliches Material: 9 Tab.
    Materialart: Digitale Medien
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  • 57
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 561-570 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: It is pointed out that if a many-electron antisymmetric wave function is expanded as a sum of spin-product functions, each multiplied by a function of coordinates, the resulting functions of coordinates have many of the same useful features found with the symmetric and antisymmetric functions representing singlet and triplet states in a two-electron system. For finding the energy, or any function of coordinates only, in the approximation in which spin-orbit interaction is neglected, one such function of coordinates can be used, the spins being disregarded. Simple procedures allow one to find matrix components of such operators as S2 and L . S from the functions of coordinates. These procedures are much easier to visualize than the use of projection operators, the permutation group, or other methods in current use. The general procedures are illustrated by application to the three-electron problem of the lithium atom, as treated by Lunell, Kaldor, and Harris, and their application to the contact hyperfine structure is pointed out.
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  • 58
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 587-602 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Propagator or Green's function methods are used to analyze the time-dependent Hartree-Fock model. The non-hermitian matrix problem for the time-dependent Hartree-Fock solution is reduced to a problem related only to hermitian matrices. Particular attention is given to the calculation of oscillator strength in different approximations. The connection between the stability of the Hartree-Fock solution and the solution of the time-dependent Hartree-Fock problem is demonstrated. The results of numerical calculations are given for aniline, azulene and pyridine.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 59
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A group-theoretical method for determining the permitted states of polyatomic molecules, proceeding from given atomic states in which the spin-orbit interaction has been taken into account, is proposed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 127-138 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Self-consistent pseudo-eigenvalue equations are explicitly derived for the iterative extended Hückel method with use of the minimum-energy criterion. It is shown that inclusion of the overlap matrix in the iterative procedure gives equations that are too complicated for the simple model under consideration. An expression for the total energy is derived, and it is shown that if the eigenvalues of the pseudo-eigenvalue equations are interpreted as ionization potentials and electron affinities, then the empirical parameters of the Hamiltonian matrix must be reinterpreted. The connection with the Hartree-Fock equations is mentioned. It is proposed that minimizing the energy in the VESCF method should be done in a manner similar to the one used in the iterative Hückel methods. Numerical applications to benzene and pyridine have been made.
    Zusätzliches Material: 5 Tab.
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  • 61
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 191-202 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: SCGF calculations are reported for the ground state of ethylene, formaldehyde, acetylene and hydrogen cyanide. A minimum basis of contracted Gaussians was used and optimum hybridization was determined for each of the molecules by systematic variation of the hybridization parameters until the total electronic energy was a minimum. Properties of CH bonds as well as CC, CO and CN σ and π bonds are discussed in some detail. The results show that the assumption of transferable framework integrals β, basic to all semiempirical methods of calculating molecular wave functions, is strictly justified within the SCGF method.
    Zusätzliches Material: 2 Ill.
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  • 62
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970) 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 63
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 315-332 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The energy bands of sodium have been calculated by the augmented-plane wave method and carried to self-consistency for both a non-spin-dependent and spin-dependent potential. The results are compared with those of previous calculations and with experimental data. It was found that the energy gaps introduced by the spin-dependent potential remained when the calculations were carried to self-consistency. Analysis of the present results involved comparison of the spin-dependent method with Löwdin's Alternant Molecular Orbital method and with Overhauser's Spin-Density-Wave model, and an analogy is drawn between the spin-dependent calculation and spin-polarized atomic calculations. By calculating the total energies as a functional of the self-consistent charge desity, it was determined that the spin-polarized crystal state had a lower energy than the state obtained from the non-spin-dependent potential. The approximations used in the calculations are discussed.
    Zusätzliches Material: 3 Ill.
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  • 64
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 4 (1970), S. 342-345 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 4 Tab.
    Materialart: Digitale Medien
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  • 65
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 19-34 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: It is demonstrated that dicarboxylic acids of uniform lengths, obtained by degrading chain-folded polyethylene single crystals, can be converted to paraffins via the intermediate diiodide by means of the procedure of Barton et al. Thus we are now in the position of obtaining uniform paraffins of chain lengths longer than hitherto available for the study of the crystallization of oligomeric chains. Measurements of melting points and heats of fusion revealed major differences between the paraffins and the corresponding parent dicarboxylic acids. It follows that such measurements on the unmodified products of the nitric acid degradation cannot be used directly for the assessment of the chain traverse length and the degree of crystallinity. It was found further, that the intermediate diiodide is a sufficiently close approximation to the paraffin for the purposes just quoted.
    Zusätzliches Material: 9 Ill.
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  • 66
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 89-103 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The theoretical justification for using M[η], or a similar quantity, as a universal calibration parameter in GPC is reviewed. The equation based on this parameter is applied to transform the primary calibration curve, obtained by means of polystyrene samples, into calibration curves for poly-α-methylstyrene, polypropylene, and linear polyethylene. The Mark-Houwink equations for these polymers, as they are used in the transformation, are discussed. The resulting GPC calibration curves are compared with molecular weights and peak elution volumes of fractionated poly-α-methylstyrene and polypropylene. The same comparison is made with samples of polypropylene and polyethylene having very broad molecular weight distributions. The agreement lies within experimental error.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 148-152 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 482-482 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 69
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 207-224 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A discussion is given of the behavior of a mathematical model chosen to approximate conditions during precipitation chromatographic fractionation of polymer (Baker Williams fractionation). With only one molecular weight species of polymer a complete solution of the mathematical model was obtained. With more than one species it was necessary to use a computer solution. Curves showing the movement of polymer containing one and two species of polymer are given for a variety of conditions of operation. It was found that the degree of fractionation of polymer approaches a limiting value with increasing length of column. Under some conditions the degree of fractionation may go through a maximum with length of column. The equilibrating distance (distance of travel of the liquid phase required to establish equilibrium of polymer between the liquid and the bed) was found to be very important in determining the fractionation.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 70
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 277-287 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Studies have been made on the dynamic and steady-shear melt rheology of an ethylene-methacrylic acid copolymer and two of its salts obtained by partial neutralization with sodium and with calcium bases. Measurements were made with a Weissenberg rheogoniometer over a broad range of shear rates and frequency in the temperature interval mainly from 100 to 160°C. The temperature coefficients of dynamic and steady shear viscosity are evaluated at both constant shear rate and constant stress. Likewise, complex dynamic viscosities and apparent high steady-flow viscosities and intercompared at equivalent frequencies and shear rates. The un-ionized acid copolymer shows good correlation between the frequency dependence of the complex viscosity and the shear rate dependence of the apparent viscosity. This is not true for either the sodium salt or the calcium salt. These results are consistent with the two-phase structural model for these materials, i.e., a matrix of hydrocarbon in which are embedded ionic domains.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 305-310 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The enchanced low-shear melt viscosity of branched polybutadienes is shown to be sensitive to dilution with low molecular compounds. The viscosity of branched polymers falls more rapidly with dilution than that of linear polymers, i.e., branched polymers show increased response to plasticization. At least one instance is demonstrated in which the viscosity ratio ηbr/ηlin reverses from a value greater than unity to less than one in passing from dry polymer to rubber extended with relatively large quantities of oil.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 72
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 371-381 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Normal stress and shear stress of concentrated polystyrene solutions in a chlorinated diphenyl were measured under steady flow and oscillatory shear flow in a Weissenberg rheogoniometer. The normal stress difference was observed to oscillate at double the frequency of the applied shear strain with amplitude proportional to the square of the applied amplitude, while the shear stress was found to oscillate at the same frequency with amplitude proportional to the applied amplitude. A theoretical relation between the displacement of the oscillatory normal stress difference from zero level and the dynamic modulus derived by Lodge and other investigators was confirmed experimentally, and the theoretical predictions of Coleman and Markovitz concerning the relation among steady-flow normal stress difference and dynamic modulus were also confirmed. However, the theoretical predictions of Lodge, of Spriggs, Huppler and Bird, and of Williams on the relation between the amplitude and phase of oscillatory normal stress and those of oscillatory shear stress did not agree with experimental results.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 47-59 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A simple method of preparing thin uniform films of high polymers has been examined for growing single crystals from solution. Single crystals of polyethylene, polypropylene, polybutene-1, polyacrylonitrile, and cellulose triacetate have been obtained by this method. Different stages of growth reveal different growth features that are also obtained from solutions of these polymers by changing temperature and concentration.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
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  • 74
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 81-87 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The high degree of flexibility of blends containing minor amounts of partly crystalline copolymers of ethylene and vinyl acetate in paraffin wax seems to be a manifestation of some type of interaction. Low-angle x-ray diffraction of such blends showed a new long spacing intermediate in length between the polymer long spacing and the c axis length of the wax unit cell. This new long spacing appears to be a consequence of isomorphism involving cocrystallization of polymeric ethylene sequences and wax molecules. A lesser type of isomorphic interaction, epitaxy, occurs in polyethylene-wax blends: wax overgrows crystals of already crystallized polyethylene in the same orientation without a change in its c axial dimension.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 75
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 143-147 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 76
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 893-901 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: We have derived from the Eyring theory of non-Newtonian flow a yield condition which is valid for an arbitrary state of stress. Experimental data obtained in simple axial compression tests show the influence of the hydrostatic stress on the yielding of poly(vinyl chloride). This fact confirms the proposed condition and disproves the von Mises criterion. Tension-torsion tests performed on thin tubes lead to results which fit our condition fairly well. The pattern of Lüders' lines appearing on the surface of thin tubes subjected to simple tension, simple shear, and tension-torsion are parallel to the direction where the value of the normal stress is equal to the hydrostatic stress.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 77
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 957-967 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The melting temperatures of homopolymers of poly(ethylene sebacate) possessing a most probable molecular weight distribution and ordered copolymers of ethylene sebacate/propylene adipate were studied by slow heating processes and by the analysis of the dependence of the melting temperature on the crystallization temperature utilizing rapid heating rates. For the ordered copolyesters, where the composition of the crystallizing co-units ranged from 0.8 to 0.2 mole fraction the latter method gave results which were similar to those that have been obtained for the other polymer systems that have been studied. Extrapolated equilibrium melting temperatures could be obtained in a straightforward manner and were found to be independent of the copolymer composition in accord with theoretical expectations. On the other hand, a unique set of results were obtained for the homopolymers. A plot of the relationship between the melting temperature and the crystallization temperature for all the molecular weights studied gave a slope close to unity. This made it operationally impossible to extrapolate to the equilibrium melting temperature for this system.
    Zusätzliches Material: 6 Ill.
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  • 78
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 999-1010 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: An investigation of the internal motion in organosilicon polymers by wideline nuclear magnetic resonance has been extended to a pair of dimethylpolysilazanes crosslinked through trifunctional silicon. The data suggest that there is considerable internal motion in all silazanes at 77°K. Evidence is presented for the presence of C3 rotation of the methyl groups, as well as rotation or torsional oscillation of the Si(CH3)2 groups about the polymer backbone. Upon warming the NMR line is seen to narrow, and this is associated with the onset of additional motion, including chain translation and chain flexing or bending. Crosslinking through silicon increases the barrier to chain translation while decreasing the barrier to chain flexing or bending.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 79
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1027-1037 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Poly-2,5-distyrylpyrazine (poly-DSP) was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and measurements of dynamic viscoelastic and electrical properties. From DTA and TGA studies it was confirmed that poly-DSP melts at 321°C and depolymerizes rapidly to the monomer at temperatures between 335°C and 345°C in helium. The polymer is affected by oxygen above 200°C. The E′ value from dynamic viscoelasticity measurements on amorphous film is 2 × 1011 dyne/cm2 at room temperature. It decrease abruptly in the temperature range 140-150°C; but the net decrease of E′ within this temperature range is relatively small. The electrical properties of amorphous poly-DSP are characterized by a small temperature dependence of the dielectric constant between room temperature and 100°C. The dielectric loss tangent was observed to be small, and the dc conductivity was extremely small. It is concluded that rotation of the phenyl branches in the polymer occurs above -30°C and the glass transition occurs at about 150°C. These properties are discussed in some detail in relation to the polymer structure.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1111-1126 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Comonomer and stereosequence distributions in linear high polymers are considered from the point of view of the general theory of stationary random sequences. Although the discussion is centered about binary polymerizations which may be regarded as stationary Markov processes of low order, attention is paid to distinguish results valid for any stationary random process including stationary non-Markov processes from those special to a particular Markov process. Alternative derivations of copolymer composition equations are given along with a corrected version of a previously suggested scheme of relating conditional probabilities of different orders. The nature and relative merits of the several measures proposed in the literature to characterize comonomer and stereosequence distributions are also discussed in some detail.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1177-1186 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The dielectric behavior of poly(vinylidene fluoride) is affected by orientation and crystal modification. The loss peak caused by molecular motion of the molecules in crystalline regions appears at about 70°C (110 Hz) (α1 absorption) for the α form, and at about 110°C (110 Hz) (α2 absorption) for the β form. Orientation significantly affects the magnitude of the β absorption which appears at about -40°C. The very high value of the dielectric constant for stretched film is believed to be due to the orientation effect. The γ absorption, which is assumed to be local-mode absorption, is not so much affected by orientation. An additional loss peak has been found at around 0°C in dynamic mechanical measurements, but the molecular mechanism is unknown.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 82
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 467-479 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A dynamic method for investigating the mechanism of permeation and diffusion through polymers has been explored. The permeation cell consists of two compartments separated by the membrane. The permeant (gas, vapor, or liquid) is introduced into one compartment; a carrier gas (helium) flows at constant rate through the other and sweeps the permeant which diffuses through the membrane to the thermal conductivity detector. Both compartments are at atmospheric pressure; thus no or little membrane support is required, and leakage problems are minimal. Moreover, the same membrane can be used over a wide temperature range and for diverse permeants. The detector signal is at any instant proportional to the permeation rate. A simple mathematical formalism for deriving the diffusion coefficient from the transient permeation rates has been developed. The measured diffusion and permeability coefficients of CO2, O2, and N2 through low-density polyethylene closely agree with literature values. Permeation of hexane and benzene through polyethylene follows a complex diffusion law, and the rate depends on the thermal history of the system. The dynamic method is particularly suited to the study of transitions in polymers. Changes in permeation rates, usually occurring at transition points, can easily be discovered by slow temperature scanning of the system.
    Zusätzliches Material: 7 Ill.
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  • 83
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 487-487 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
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  • 84
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 519-528 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Three transitions are detected dilatometrically when partially isotactic poly(propylene oxide) melts. One transition, the temperature of which is independent of the crystallization temperature over a wide range below 60°C, is ascribed to the melting of lamellar crystallites which are limited in thickness by the average isotactic sequence length alone. The other two transitions, the temperatures of which vary with the crystallization temperature, are ascribed to the melting of lamellar crystallites with thickness determined predominantly by three- and two-dimensional primary nucleation acts. The theory of Flory is adapted and applied quantitatively to the melting points of three crystalline fractions of poly(propylene oxide), obtained from a polymer produced via the zinc diethyl and water catalyst system. This method leads to a thermodynamic melting point of isotactic poly(propylene oxide) near 82°C.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 583-594 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Characteristic markings of concentric bands are formed on the fracture surface of tensile specimens under certain loading conditions. The marking form in the fast crack growth region of the mirror area of fracture. Optical and electron optical microscope techniques have been used to study the morphology of the markings. It is shown that in this region the crack propagates along the interface between the craze, in which the crack nucleated, and the bulk material. The mackerel pattern is caused by the crack jumping from one craze-matrix interface to the other.
    Zusätzliches Material: 13 Ill.
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  • 86
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 605-624 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Incorporation of plasticizers or other inert, liquid diluents causes a profound weakening of rubbers. The modulus of elasticity and tensile strength decrease approximately with the square of the gel fraction v0 of rubber which was present at the time of formation of the three-dimensional network. Equlibrium swelling of plasticized rubbers is well represented by v2m = kv0, where v2m is the volume fraction of rubber network in the swollen state, at equlibrium, and k a constant equal to v2m for the unplasticized rubber. This swelling law is independent of the way in which v0 is obtained; inert liquid diluents, comprising molecularly dispersed compounds, as well as suspensions of insoluble liquids, gases, and chemically inert, solid fillers yield the same relation. Further, it is independent of the chemical nature of solvent and rubber. It appears that also the mechanical properties of foams, liquid-filled foams, and plasticized elastomers containing the same volume fraction of network rubber are very similar.
    Zusätzliches Material: 7 Ill.
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  • 87
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 649-652 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 88
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 657-678 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: On axial extension of polymer melts at constant deformation rates, the development of high-elastic deformation is of predominant importance during the initial period. High-elastic deformation is accompanied by a rise in viscosity and in the modulus of high-elasticity and by retardation of the relaxation processes in the region of large relaxation times. At relatively low deformation rates, the rise in viscosity and high-elasticity modulus and the retardation of relaxation processes may give way to a decrease in viscosity and high-elasticity modulus and acceleration of relaxation processes, so that stationary flow regimes are attained. The transition from strain regimes with increasing viscosity and modulus of high elasticity to those with a decrease of these quantities corresponds to an increase in the rate of accumulation of irreversible deformation. Accordingly, a competing influence due to the orientation effect and to destruction of the network of intermolecular bonds becomes evident while stationary flow is being attained. The orientation effect must be responsible for the retardation of the relaxation processes, whereas rupture of the intermolecular network bonds results in structural relaxation accelerating relaxation processes. In contrast to shearing, during extension the orientation effect is of predominant importance. Hence in stationary flow regimes the viscosity may not only remain independent of the rate of strain, but even increase with it. In this case the contribution of the large relaxation times to the relaxation spectrum increases with increasing stress in stationary flow regimes. The fact that the longitudinal viscosity and the modulus of high elasticity are independent of the stress in stationary flow regimes does not guarantee linearity of the mechanical properties of the polymer in the prestationary stage of deformation when complex changes occur in its relaxation characteristics. At high deformation rates the viscosity and the modulus of high elasticity keep rising with increasing deformation until rupture occurs. Determination of the strength of polystyrene samples vitrified after extension showed that it is due not to the entire degree of extension, but only to the value of accumulated high-elastic deformation. The strength of the vitrified samples is to a first approximation independent of the rate at which the melt was extended.
    Zusätzliches Material: 19 Ill.
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  • 89
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 727-738 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Dielectric relaxation data have been obtained for two ethylene-methacrylic acid copolymers (containing about 4 mole-% methacrylic acid units and about 8 mole-% methacrylic acid units, respectively) and the lithium, sodium, and calcium salts prepared by partial neutralization of the polyacids. The frequency range employed was from 50 Hz to 10 kHz and the temperature range was from -130°C to 100°C. Attention is focused on three dielectric loss regions labeled β, β and α in order of increasing temperature. The β′ process (-10°C at 100 Hz in the salts only) correlates with a mechanical loss process previously reported and is attributed to microbrownian motion taking place in an amorphous hydrocarbon phase. The β′ process (20°C at 100 Hz) has also been observed mechanically and is attributed to the same mechanism as the β process. The higher temperature of this relaxation compared to the β relaxation is attributed to the presence of acid groups which form crosslinks composed of interchain hydrogen bonds. The α process (〉50°C at 100 Hz in the salts only) correlates with dielectric and NMR data previously reported for a sodium salt and is assigned to motions within ionic domains formed by the clustering of salt groups.
    Zusätzliches Material: 7 Ill.
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  • 90
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 807-811 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 91
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 815-816 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
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  • 92
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Sedimentation equilibrium in the ultracentrifuge means that there is such a distribution of molecular species throughout the cell, that the centrifugal forces are balanced by differences in the activities. This provides a method for determination of the activities and the chemical potentials in polymer solutions which, in principle, is very simple and reliable. A complication is caused by polydispersity of the dissolved polymer. If one assumes that the interaction parameter depends on concentration and temperature, but not on molecular weight, it is possible to determine the chemical potential of polymer and solvent from the ultracentrifugal data. Experiments have been carried out on the systems polystyrene-toluene and polystyrene-cyclohexane at different temperatures and in the concentration range 0-80 wt-%. The results are expressed in the data for the chemical potential of the solvent, the number average chemical potential of the polymer and the interaction parameter χ.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 921-935 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Several partially interpenetrating polymeric networks (IPN) were made by combining chemically different linear elastomers. The polymer combinations were deposited as films from aqueous emulsions made by mixing the individual emulsions in equal proportions. The films were crosslinked to form two superimposed networks. In two cases, the networks were cleanly separated by hydrolysis of one of the component networks to demonstrate that there was no chemical interaction between the polymers. Measurement of crosslink density showed that, in most cases, partial interpenetration does occur as evidenced by an effective crosslink density of the IPN's greater than the arithmetic mean of the crosslink densities of the component networks. The swelling ratios, densities, and stress-strain properties were determined. For one of the network combinations, a poly(urethane-urea) and a poly(butadiene-acrylonitrile), a series of IPN's varying in polymer composition was made. The swelling ratios and densities are close to the arithmetic means; however, both the tensile strength and crosslink density exhibit a maximum at about 70% poly(butadiene-acrylonitrile). The maximum tensile strength is actually significantly higher than that of either of the component polymers. The elongations all approach that of the poly(urethane-urea), the more extensible material, except for compositions approaching 100% poly(butadiene-acrylonitrile), which exhibit a very low extensibility.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 969-977 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Characteristic wide-line proton magnetic resonance absorption spectra of a number of representative cellulose preparations have been obtained in the dry state and after addition of about 7% water. Line widths, second moments, spin-spin and spin-lattice relaxation times have been determined. The second moment of the absorption curve of dry cellulose was found to correlate well with the crystalline fraction for most specimens. A technique is described for determining the number of water-cellulose protons exchanging relative to the number of cellulose protons not exchanging. The reduction in absorption line width observed when water is added to cellulose is shown to be quantitatively consistent with such a proton exchange phenomenon.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1755-1772 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The morphology of selenium has been studied in light of present concepts of crystallinity in crystalline organic polymers. Spherulitic crystallization and resultant morphology were examined as a function of temperature by transmission and replication electron microscopy, electron diffraction, and optical microscopy. Evidence is given for polymer chain folding during crystallization of trigonal selenium. Theoretical thermodynamic calculations presented yield several thermodynamic values including an equilibrium melting point of 219.2°C, a fold surface energy of 337 ergs/cm2 and a lateral surface energy of 9.8 ergs/cm2.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1803-1821 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Various procedures for universal calibration in gel-permeation chromatography with polystyrene gels are examined for polystyrene and polydimethylsiloxane fractions. For o-dichlorobenzene at 138°C, experimental intrinsic viscosity-molecular weight data show that the Mark-Houwink exponents are 0.70 and 0.57 for polystyrene and polydimethylsiloxane, respectively. In principle, this difference permits a distinction between the various polymer size parameters proposed for universal calibration. An interpretation of the experimental polydimethylsiloxane calibration for o-dichlorobenzene at 138°C requires a consideration of errors in average molecular weights and errors arising from the use of average molecular weight instead of peak molecular weight. When calibration procedures utilizing hydrodynamic volume and unperturbed dimensions are examined, the difference between them is comparable with experimental error. If the Flory-Fox viscosity expression is employed, the perturbed end-to-end distance (or radius of gyration) and the hydrodynamic volume give equivalent universal calibrations. The experimental data are sufficiently accurate to show that the perturbed dimension determined with the Ptitsyn-Eizner relation does not give an adequate universal calibration.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1545-1564 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Crystallization of compression-molded isotactic polypropylene and polyethylene is invariably spherulitic; generally, nucleation occurs randomly throughout the sample. In a special case where nucleation predominates at the surface, spherulitic growth centers become crowded and are forced to propagate unidirectionally into the bulk (transcrystallinity). Conditions for the formation of transcrystallinity have been investigated by optical and scanning electron microscopy. The occurrence of transcrystallinity is attributed to heterogeneous nucleation induced at the mold surface. To be effective, the mold surface must have a nucleating efficiency equal to or greater than that of adventitious nuclei present in the polymer. As the crystallization temperature approaches the melting point, the activity of mold surfaces is found to increase leading invariably to transcrystalline formation. The degree of activity of various mold surfaces correlates with the known activity of specific dispersed nucleating agents having similar chemical structures. Contrary to claims in the literature, the surface energy of the mold surface and temperature gradients across the melt surface do not play a primary role in transcrystalline formation of polypropylene.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1909-1916 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The flow behavior of α,ω-dihydroxypolydimethylsiloxanes, having a weight-average number-average molecular weight ratio of 1.1-1.2, was studied with a Cannon-Manning viscometer and an Instron rheometer. Comparison of the flow behavior of samples with narrow and broad molecular weight distributions indicated that the onset of non-Newtonian behavior occurred at a much higher shear rate for narrow-distribution polydimethylsiloxanes than for polydisperse polydimethylsiloxanes. A plot of reduced viscosity versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma \eta _0 {M \mathord{\left/ {\vphantom {M T}} \right. \kern-\nulldelimiterspace} T} $\end{document} gave two experimental master curves, one for polymer of narrow distribution and the other for polydisperse polymer. The experimental master curve obtained from the narrow-distribution polymer was found to fit the theoretical master curve derived from Graessley's entanglement theory. The viscosity-molecular weight relationship for the higher molecular weight polydimethylsiloxanes was found to be the same for both hydroxydimethylsilyl- and trimethylsilyl-endblocked polymers. However, at low molecular weight, the viscosity-molecular weight curve deviated from linearity because of the association of polydimethylsiloxanols, which apparently is not significant at higher molecular weights. The critical molecular weight of entanglement, Mc, was found to be about 30,000.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 99
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1937-1953 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: It has been considered for some time that the presence of birefringence in an oriented polymer must affect the light-scattering behavior. Previous analyses of this phenomenon are restricted to single-particle scattering. A more complete theory of the effect of birefringence on the scattering of light from correlated systems is presented. The measured scattering intensity is shown to be dependent upon the optical properties of the sample as well as the experimental technique and conditions.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 2029-2032 
    ISSN: 0449-2978
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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