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  • 1990-1994  (6)
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Material
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Ultraviolet photoemission study of oligothiophenes: π-band evolution and geometries (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4077-4092 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ultraviolet photoelectron spectroscopy (UPS) has been applied to the investigation of the electronic structure of oligothiophenes with 4–8 thiophene rings. In a series of α-linked oligomers (αn with n being the number of rings), a systematic evolution of the π band is observed. Several peaks which correspond to the π band are observed in the region of 0.7–3 eV below the Fermi level (EF), and the bandwidth becomes broader with increasing n. The nonbonding π band is observed at 3.5 eV below EF and its energy is almost independent of the number of thiophene units. UPS spectra of α7 and α8 are fairly similar to the spectra of polythiophene, showing that these oligomers are good model compounds of the polymer. The ionization threshold energy of α7 and polythiophene was observed to be 5.3 eV. The effect of irregularity on the π-electron system was also studied by using oligomers which contain a β linkage or a vinylene group at the middle of the molecule. The UPS spectra showed that the β linkages significantly affect the electronic structure of polythiophene, while the vinylene group does not. In order to analyze the UPS spectra and to investigate the electronic structures of oligomers, the orbital energies and the geometries of these oligomers are calculated by the semiempirical MNDO-SCF-MO (modified neglect of diatomic overlap self-consistent-field molecular orbital) method. Theoretically simulated spectra of these oligothiophenes derived from the obtained orbital energies by Gaussian broadening are compared with the observed ones. The agreement between the observed and calculated spectra is very good, particularly in the π region. It is shown from the optimized geometry that (1) αn 's have planar structure and π electrons are delocalized, (2) the oligomer with β linkages has nonplanar structure leading to limited delocalization of π electrons, and (3) the oligomers with a vinylene group are almost planar and the disturbance by the vinylene group on the delocalization is small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458561
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Development of Si-B-O-N fibres from polyborosilazane (1994)
    Springer
    Journal of materials science 29 (1994), S. 2238-2244 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A polyborosilazane, which is a precursor of ceramic fibre, was synthesized from perhydropolysilazane and trimethyl borate. The polyborosilazane was dry-spun and then pyrolysed to produce amorphous Si-B-O-N fibre. The Si-B-O-N fibre retained its high tensile strength to higher temperatures (about 1600 °C). The fibre has a density of 2.4 g cm−3, tensile strength of 2.5 GPa and an elastic modulus of 180 GPa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01154704
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    121Sb Mössbauer spectroscopic study of a series of organoantimony(III) compounds (1992)
    Springer
    Hyperfine interactions 68 (1992), S. 197-200 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A systematic study of organoantimony(III) compounds, SbR3, was attempted in view of the effect on Mössbauer parameters of the substituent on the aromatic ring. The Mössbauer parameters obtained in frozen organic solutions reflected the electronic effect caused by the characteristics of the substituents, electron donative or attractive, at the para position on the aromatic ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396470
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Chemical states of57Fe-atoms after ec-decay of57Co-labelled Co(BrO3)2·6H2O studied by coincidence Mössbauer spectroscopy (1992)
    Springer
    Hyperfine interactions 70 (1992), S. 1241-1244 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two kinds of time differential Mössbauer spectra of57Co-labelled Co(BrO3)2·6H2O were measured at room temperature by delayed coincidence technique, i.e., one was the delayed coincidence between 122 keV γ ray and 14.4 keV γ ray (γ, γ-ray coincidence), and another was the coincidence between 6.3 keV KX ray and 14.4 keV γ ray (X, γ-ray coincidence). The time dependence of chemical states of57Fe-species were observed on γ, γ-ray and X, γ-ray coincidence Mössbauer spectra. The relative area intensities of57Fe(II) observed on the X, γ-ray coincidence spectra were larger than those on the γ, γ-ray coincidence spectra on every time windows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02397554
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Systematic behavior of mass-yield curves in low-energy fission of actinides (1990)
    Springer
    Journal of radioanalytical and nuclear chemistry 142 (1990), S. 231-251 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Mass yield curves of spontaneous fissions, thermal-neutron induced fissions, monochromatic-neutron and proton induced fissions of actinides are reviewed. Mean masses of light and heavy asymmetric mass yield peaks are listed. The subtle change of the shape of the asymmetric heavy peak is expressed in terms of the parameters of two Gaussians that fit the observed data well. One Gaussian is narrow in width and always peaks at A=133–136 while the other is broader and peaks at A=140−144. The FWHM of the heavy asymmetric peak becomes minimum for the fissioning mass A=240−245. An analysis of the projectile energy dependence of mass yield curves indicated, at least, two distinctively different behaviors, one for asymmetric products and the other for symmetric products. From the energy dependence of the peak-to-valley rations, the “extra-energy” required for symmetric mass division, or the difference in the fission barrier heights, in the nomeuclature of the two-mode hypothesis, is deduced for a wide range of fission nuclides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02039465
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Simultaneous determination of rhenium, osmium and iridium in meteoritic samples by neutron activation analysis using simple and effective radiochemical procedures (1994)
    Springer
    Journal of radioanalytical and nuclear chemistry 185 (1994), S. 3-13 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Simple and effective procedures for the determination of Re, Os and Ir by radiochemical neutron activation analysis are presented. Those elements are separated individually by distillation (for Os) and anion exchange techniques (for Re and Ir) for a single specimen. Reproducibilities of the data obtained by the present procedures are evaluated by replicate analyses of the Allende meteorite sample, and are deduced to be 3% for Re, 6% for Os and 4% for Ir (1σ). Detection limits for the present procedures are calculated to be 1 ppb for Re, 20 ppb for Os and 5 ppb for Ir. These procedures were applied to Antarctic meteorites and proved to work very effectively for the determination of trace Re, Os and Ir in chondrite meteorites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042947
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    Paper (German National Licenses)
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