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1.
Whitten AE Dittrich B Spackman MA Turner P Brown TC 《Dalton transactions (Cambridge, England : 2003)》2004,(1):23-29
High-resolution X-ray diffraction data have been collected on the cubic polymorph of antimony(III) oxide (senarmontite) to determine the charge distribution in the crystal. The results are in quantitative agreement with crystal Hartree-Fock calculations for this polymorph, and have been compared with theoretical calculations on the orthorhombic polymorph (valentinite). Information about the nature of bonding and relative bond strengths in the two polymorphs has been extracted in a straightforward manner via topological analysis of the electron density. All the close contacts in both polymorphs are found to be similar in nature based on the value of the Laplacian, the magnitude of the electron density and the local energy density at the bond critical points, and these characterise the observed interactions as substantially polar covalent, similar to molecular calculation results on Si-O and Ge-O. Electrostatic potential isosurfaces reveal the octopolar nature of this function for senarmontite, and shed light on the observed packing arrangement of Sb4O6 molecules in the crystal. 相似文献
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The TO, LO and TA phonon assisted luminescence lines associated with carrier recombination inside an electron-hole drop in Si have been studied. The carrier density n and the droplet binding energy ø per electron-hole pair have been estimated from the lineshape and position of the TA-phonon assisted line. The resulting values n = (3.0±.1) × 1018cm-3 and ø = 7.9±.1 meV are smaller than previously published values based on an analysis of the unresolved TO-LO line. The discrepancy in the fitted density arises because the TO-LO line is broader than the sum of two TA lines separated by the known TO-LO splitting at any intensity ratio. The effect of LO phonon dispersion can explain the effect, if a TO-LO intensity ratio close to unity is assumed, contrary to previously expressed theoretical expectations. 相似文献
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Niels Olaf Østerberg Torben Smith Sørensen Jørgen Birger Jensen 《Journal of Electroanalytical Chemistry》1981,119(1):93-108
The emf of electrochemical cells containing various sorts of salt bridges between various concentrations has been measured. The net diffusion potential over a salt bridge has been treated theoretically. An expression to calculate the net diffusion potential has been derived and tested on values estimated from the emf measurements. A merit factor has been calculated for a saturated KCl bridge separating two HCl solutions and compared with the merit factor estimated from emf measurements on the cell:Pt|Ag|AgCl, HCl(c1)|KCl(sat)|HCl(c2), AgCl|Ag|Pt The practical performance of two commonly used reference electrodes with salt bridges has been tested on emf measurements on KBr solutions. 相似文献
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Anatol P. Spork Stefan Koppermann Birger Dittrich Regine Herbst-Irmer Christian Ducho 《Tetrahedron: Asymmetry》2010,21(7):763-766
The reaction of protected uridine 5′-aldehydes with sulfur ylides has been reinvestigated. Further transformation of the resulting epoxide product provided a compound of which a single crystal for X-ray diffraction was obtained. As a consequence from the elucidated structure, the stereochemical configuration of the epoxide furnished by the sulfur ylide reaction was revised. Based on these results, an efficient synthesis of the core structure of the naturally occurring muraymycin and caprazamycin nucleoside antibiotics was developed. 相似文献
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