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  • Chemistry  (1)
  • PACS. 61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. - 61.50.Ks Crystallographic aspects of phase transformations; pressure effects - 61.66.Bi Elemental solids  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 17 (2000), S. 227-233 
    ISSN: 1434-6036
    Keywords: PACS. 61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. - 61.50.Ks Crystallographic aspects of phase transformations; pressure effects - 61.66.Bi Elemental solids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Bromine has been studied up to a pressure of 110 GPa by X-ray absorption spectroscopy (XAS) at the bromine K-edge, that allows to measure the pressure evolution of the width of the unoccupied conduction band. At GPa we observe a slope change in the evolution of this width. Comparison with published calculations of the electronic density of states indicates that the physical origin of the slope change is compatible with the metallisation process. This is also confirmed by a simple tight binding calculation. In addition, the metallisation pressure value is in agreement with calculated ones. At GPa a discontinuity in the evolution of the width of the sigma antibonding band points out the onset of a phase transformation. This result is compatible with the observed phase transformation near GPa by X-ray diffraction that is associated with the molecular dissociation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Although nitrogen inversion in unsubstituted aziridines has been shown by 1H NMR, it was only possible to study quantitatively the distribution of both invertomers and determine the thermodynamic parameters by a systematic high field NMR study (CAMECA 250 MHz). Thermodynamic parameters have been determined for 32 compounds. In C-aryl aziridines, the steric hindrance of the aromatic group and its variation with other aziridine ring substituents can be studied. These observations are in agreement with a conjugation phenomenon between the aromatic system and the aziridine ring.
    Notes: Bien que le phénomène d'inversion de l'azote dans les aziridines secondaires ait pu être mis en évidence par RMN 1H, seule une étude systématique à 250 MHz a permis d'étudier quantitativement la répartion des deux invertomères et ainsi, de déterminer les paramètres thermodynamiques liés à l'équilibre conformationnel. Ces paramètres ont été déterminés pour 32 composés. Dans les aziridines C-phénylées, une variation de l'encombrement du groupement aromatique en fonction des autres substituants du cycle aziridine peut être mis en évidence. Ces observations prouvent l'existence d'un phénomène de conjugaison entre système aromatique et petit cycle. phénomène préalablement mis en évidence par effet Faraday.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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