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  • Physics  (30)
  • Atomic, Molecular and Optical Physics  (7)
  • Wiley-Blackwell  (37)
  • National Academy of Sciences
  • 1975-1979  (37)
  • 1976  (37)
Collection
Keywords
Publisher
  • Wiley-Blackwell  (37)
  • National Academy of Sciences
Years
  • 1975-1979  (37)
Year
  • 1
    Electronic Resource
    Electronic Resource
    The instabilities of the Hartree-Fock solutions and the lattice instabilities for conjugated hydrocarbons: The bond-order and bond-length alternations (1976)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 917-935 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The instabilities, especially the singlet instabilities, of the conventional Hartree-Fock (HF) solutions for a variety of alternant and nonalternant hydrocarbons, some of which have been known to show lattice instabilities (bond-length alterations), are examined. The HF solutions for nonalternant hydrocarbons in the pentalene series larger than heptalene and [4n + 2]-annulenes larger than C22H22 are found to be singlet unstable and there appear new solutions lower in energy than the conventional HF solutions and characterized by charge-density waves exhibiting bond-order alterations. It is found that such symmetry-breaking solutions are energetically further stabilized by distorting the nuclear framework so that it may match up with the distribution of bond-order matrix elements of the charge-density wave, which means that in conjugated systems the singlet instability of the HF solution is always accompanied with the lattice instability. Further, it is shown that in conjugated systems, even when the HF solution is singlet stable, if it is not sufficiently stable as, for example, in pentalene and heptalene, there is every possibility for the occurrence of lattice instability. It is also shown that the singlet instability as well as the lattice instability arises from the existence of a sufficiently low-lying singlet excited state.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560100520
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  • 2
    Electronic Resource
    Electronic Resource
    Investigation of relaxation processes in linear polyethylene in the 10-9 sec region by means of high-resolution neutron spectroscopy (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1351-1359 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Results are presented of neutron incoherent scattering experiments on isotropic linear polyethylene samples of high (80%) and low (48%) crystallinity in the temperature range between -180°C and +85°C for values of the scattering vector between 0.29 Å-1 and 1.81 Å-1 obtained with a high resolution backscattering spectrometer (Δħω = 0.25 - 1.0 μeV) and between 0.57 Å-1 and 2.4 Å-1 with a time-of-flight spectrometer (Δħω = 420 μeV). From a comparison of the results on these samples one concludes that relaxation takes place predominantly in the noncrystalline regions. This motion cannot be adequately accounted for by any of the existing models for the γ-process. Therefore, a more liquidlike motion is suggested. Diffusion of shorter chain segments has also been ruled out since it is too slow to be observed. A simplified model of protonic jumps between equidistant sites located on the periphery of a circle of radius 2.5 Å reproduces the experimental results well. For the average time between successive CH2-group reorientations one obtains τ1 = τ0 exp(EactRT) with τ0 = (2.0 ± 1.5) × 10-13 sec and Eact = (4.5 ± 1.0) kcal/mole. The values join up well with those for the γ-process observed by NMR. It has been concluded that 60-90% of the protons in the noncrystalline regions participate in this motion.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1976.180140801
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  • 3
    Electronic Resource
    Electronic Resource
    Supported catalysts for stereospecific polymerization of propylene (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 14 (1976), S. 1915-1932 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrabenzyltitanium (B4Ti), tribenzyltitanium chloride (B3TiCl), tetra(p-methylbenzyl)titanium (R4Ti) and tri(p-methylbenzyl)titanium chloride (R3TiCl) have been used as catalysts for ethylene and propylene polymerization activated by AlEt2Cl. B4Ti-AIEt2Cl in solution polymerizes ethylene readily but its activity decays rapidly. B4Ti was also supported on Cab-O-Sil, Alon C, and Mg(OH)Cl. The last support was found to give catalyst with longest lifetime with a rate of polymerization, Rp = 7.0 g/hr-mmole Ti-atm ethylene. 14CO counting techniques gave 1.13 × 10-3 mole of propagating center per mole of B4Ti; the rate constant of propagation, kp = 540 l./mole-sec. None of the tetravalent titanium compounds polymerize propylene in solution. However, when supported on Mg(OH)Cl, Cab-O-Sil, Alon C, Cab-O-Ti, and charcoal, they all polymerize propylene. In this work the supports were characterized by various techniques, including the paramagnetic probe method, to determine the concentration and nature of surface hydroxyls. Those factors controlling the rate and stereospecificity of propylene polymerization were investigated. The system B3TiCl-Mg(OH)Cl-AlEt2Cl is the most active with Rp = 2.89 g/hr-mmole Ti-atm propylene. The concentration of propagation center is 0.9 × 10-3 mole per mole of B3TiCl; kp = 32 l./mole-sec. This catalyst gave only about 70% stereoregular polymer. Diethyl ether is found to raise stereospecificity to 100%, but there is a concommittent tenfold decrease of activity. Other interesting catalyst systems are: (π-C5H5)TiMe3-Mg(OH)Cl-AlEt2Cl (1.56, 89.5); (π-C5H5)TiMe2-Mg(OH)Cl-AlEt2Cl (0.075, 94.5); and (π-C5H5)TiMe3-Alon C-Al-Et2Cl (0.08,97.2), where the first number in the parenthesis is Rp in g/mmole Ti-hr-atm and the second entry corresponds to percentage yield of stereoregular polypropylene. Hafnocene and titanocene supported on Mg(OH)Cl produce only oligomers of propylene.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1976.170140809
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  • 4
    Electronic Resource
    Electronic Resource
    Interaction of poly(vinyl alcohol), boric acid, and iodine (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 14 (1976), S. 2319-2320 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1976.170140920
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  • 5
    Electronic Resource
    Electronic Resource
    Generation of genealogical spin eigenfunctions (1976)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 143-149 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is given for generating the Yamanouchi-Kotani genealogical spin eigenfunctions which requires neither storage of eigenfunctions for smaller numbers of electrons, nor summations of large order, nor explicit use of results from the theory of representations of the symmetric group. An explicit formula is given for the coefficients of expansion in terms of spin products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560100112
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  • 6
    Electronic Resource
    Electronic Resource
    Calculated anisotropies in the fermi surface of alkali metals (1976)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 261-280 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The densities of states and Fermi energies were accurately calculated from E(k) data obtained by the self-consistent-band Augmented Plane Wave (APW) method, using a quadratic energy expansion. The reliability of the Monte Carlo integration was investigated. It was sufficiently good to determine the anisotropy of the Fermi surface of lithium, sodium, and potassium.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560100207
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  • 7
    Electronic Resource
    Electronic Resource
    Many-electron theory in the Waller-Hartree spin-free method (1976)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 791-797 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A many-electron theory is developed for the determination of pure spin state wave-functions and energies to avoid the difficulties in doing integration. The Waller-Hartree pure spin state wave-functions are very convenient for this purpose. The required explicit formulas for the values of the Waller-Hartree wave-functions Y(S, M) and HY(S, M) at some physical points are produced, where local orthonormal orbitals are used to simplify the calculation of HY(S, M). A method for the construction of these orbitals is given, and a transformation formula is also given to show the interchangability between the local energy expression and the conventional expectation energy integral.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560100510
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  • 8
    Electronic Resource
    Electronic Resource
    Calculation of intermolecular interactions within the PCILO framework (1976)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 909-916 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The PCILO method was used to calculate the intermolecular interaction of London-van der Waals type, hydrogen bonding type, and charge transfer type interactions, respectively. The stabilization energies of the calculated supermolecules are: 0.85 kcal · mole-1 for the nonane dimer,4.15 kcal · mole-1 for the water dimer, and3.60 kcal · mole-1 for the butene-2-cis-Li+ complex.The analysis of the individual contributions of the energy reflects well the mechanism of the intermolecular interaction.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560100519
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  • 9
    Electronic Resource
    Electronic Resource
    Exclusion principle and the symmetry adapted wave-functions (1976)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 299-305 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Wave-functions of various spin-dependent and spin-free methods are examined from the point of view of the requirements of the exclusion principle and the spin projection. It is shown that the “two-rowed” or “two-columned” requirements of the standard Young tableaux are necessary but not sufficient to replace the “antisymmetry” requirement of a wave-function and to be regarded as exclusion principle. The symmetry adapted wave-functions which are constructed from the matric basis ers[λ] may not satisfy the exclusion principle and, hence, their usages are open to question. The appropriate symmetry adapted wave-functions which satisfied the exclusion principle are given for any pure spin state. We have also shown that the structure operators NirPir for bond functions are spin projectors in the Waller-Hartree double-antisymmetrized space only, and should not be used in the Hartree product space. Furthermore, if the corresponding matric operators PirNirPir are used in the Hartree product space, then the wave-functions thus constructed may not be antisymmetric with respect to the permutations of indistinguishable electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560100209
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  • 10
    Electronic Resource
    Electronic Resource
    Upper and lower bounds to critical values of the Hartree operator (1976)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 10 (1976), S. 985-992 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Upper and lower bounds for the minimal critical energy E of the Hartree operator for helium are calculated. We show that a Ritz analogous procedure for the calculation of the upper bounds converges to the exact value. The lower bound to E yields that the ground state EH of the helium atom is strictly lower than 2E.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560100609
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