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  • 1995-1999
  • 1990-1994  (3)
  • 1985-1989
  • 1990  (3)
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  • 1995-1999
  • 1990-1994  (3)
  • 1985-1989
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  • 1
    Electronic Resource
    Electronic Resource
    Vibronic perturbations in the A˜ 2Πu–X˜ 2Πg transition of BO2: K-resonance crossings and the onset of chaotic behavior (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2848-2861 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed re-investigation of the (0,0) and 211 bands of the A˜ 2Πu–X˜ 2Πg transition of 11BO2, near 545 nm, has been carried out from spectra taken at sub-Doppler resolution. Avoided crossings are found to occur between the 2Σ and 2Δ vibronic components of the v2=1 level of the A˜ 2Πu state. These perturbations are the first known examples of K-resonance crossings, which result from an interplay of the electronic Λ-type doubling and the vibrational l-type doubling in a state where the electrostatic parameter ε is small. It turns out that perturbations of this type must always occur in a 2Π electronic state if the ratio A/εω2 is large enough, but have not been seen until now for lack of suitable data. Their existence allows an unusually complete description of the orbital angular momentum effects in both the A˜ 2Πu and X˜ 2Πg states. It has been necessary to fit the avoided crossings by a full matrix treatment of the K resonance. In addition the A˜ 2Πu state, although it appears to be unperturbed at lower resolution, shows an astonishing number of very small random rotational perturbations. These arise from vibronic coupling between the A˜ 2Πu and X˜ 2Πg states of BO2 through the ν3 vibration, which has species σ+u; their presence is consistent with the explanation given by Kawaguchi et al. [Mol. Phys. 44, 509 (1981)] for the sizable negative anharmonicity of the ground state ν3 vibration. About 20% of the available ground state energy levels at 18 300 cm−1 appear to be active in causing level shifts and splittings in the A˜ 2Πu state. The matrix elements are quite small, ranging up to about 600 MHz, but the great number of perturbations indicates the onset of chaotic behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457931
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    Paper (German National Licenses)
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  • 2
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    An Early Polish Advocate of Slavic Unity. The Views and Activities of Stanislaw Staszic (1755-1826) and his views on Russia and Her Destiny in the Post-Napoleonic Period (1990)
    Boulder : Periodicals Archive Online (PAO)
    East European quarterly. 24:1 (1990:Spring) 1 
    Details
    ISSN: 0012-8449
    Topics: Political Science
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:b094-1990-024-01-000001
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  • 3
    Electronic Resource
    Electronic Resource
    Darstellung und Kristallstruktur der Pnictidoxide Na2Ti2As2O und Na2Ti2Sb2O (1990)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 584 (1990), S. 150-158 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation and Crystal Structure of the Pnictide Oxides Na2Ti2As2O and Na2Ti2Sb2ONa2Ti2As2O and Na2Ti2Sb2O were synthesized in form of very easily hydrolysed metallic-grey powders by reaction of Na2O and TiAs resp. TiSb in sealed tantalum tubes under argon. The tetrahedral bodycentered crystallizing compounds from a modified anti-K2NiF4 structure type [1] (also called Eu4As2O-type [2,3]), space group I4/mmm (no. 139), with the lattice constants for Na2Ti2As2O: a = 407.0(2) pm, c = 1528.8(4) pm and for Na2Ti2Sb2O: a = 414.4(0) pm, c = 1656.1(1) pm.Magnetic measurements of powder samples of Na2Ti2Sb2O show antiferromagnetic interaction within the Ti - O-layers. Superconductivity was not found by ac-shielding method down to 4 K.
    Notes: Durch Umsetzung von Na2O und TiAs bzw. TiSb in verschweißten Tantalampullen unter Argon gelang die Darstellung der metallisch grauen und sehr hydrolyseempfindlichen Verbindungen Na2Ti2As2O bzw. Na2Ti2Sb2O. Sie kristallisieren tetragonal innenzentriert in einem modifizierten anti-K2NiF4-Typ [1] (modifizierter Eu4As2O-Typ [2, 3]), Raumgruppe I4/mmm (Nr. 139) mit den Gitterkonstanten für Na2Ti2As2O: a = 407,0(2) pm, c = 1528,8(4) pm und für Na2Ti2Sb2O: a = 414,4(0) pm, c = 1656,1(1) pm.Magnetische Messungen an Pulverproben von Na2Ti2Sb2O weisen auf antiferromagnetische Wechselwirkungen innerhalb der Ti - O-Schichten hin. Ein Test auf supraleitende Eigenschaften nach der AC-shielding-Methode erbrachte bis zu Temperaturen von 4 K keinen Hinweis für das Auftreten von Abschirmströmen.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19905840115
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