An optical study of the stretching absorption band near 3 microns from OH- defects in LiNbO3

A near infrared absorption band (λ = 2.87 μ), identified as the 0–1 stretching vibrational band of OH^- defects in LiNbO₃, has been observed at 6, 77, and 300 K. This band was completely polarized perpendicular to the crystallographic c-axis within experimental error and two peaks, separated by approximately 13 cm^?1, were resolved. Both the structure and optical anisotropy of this band were independent of stoichiometry and sample treatments and may be understood in terms of a simple model where protons are captured by O^2- anions forming OH^- defects whose orientations are determined by neighboring O^2- ions.     

Bildgarben und Fasercohomologie für Relativ Analytische Räume

Let : XY be a relative analytic space and an _X module. The object of this paper is to collect some results on the connection between the fibre cohomology groups Hⁱ(X(y),(y)) and the direct image sheaves Rⁱ _*. This generalizes results of Kodaira-Spencer and Grauert-Riemen-schneider giving a unified approach based on the methods of [9].     

NMR study of structure and dynamics of stereocomplexes of poly(methyl methacrylate) in C6D6 and CD3CN

Summary Stereocomplexes of isotactic (i) and syndiotactic (s) poly(methyl methacrylate)(PMMA), with different stereoregularity of thes-PMMA component, in C₆D₆ and CD₃CN solution were investigated by means of¹H NMR spectra measured with magic angle spinning (MAR-NMR), broadline (BL) NMR spectra and¹³C NMR spectra measured with strong proton decoupling. This study has shown that in associated segments of the stereocomplexes withp= 30–40% (p is the fraction of associated monomer units) the-CH₃ and CH₂ groups exhibit equal mobility as in solutions of onlyi ors PMMA, but in consequence of interaction of the ester groups these motions are restricted in space. In complexes with high density of interactions (p 75%) the motion of-CH₃ and CH₂ groups in associated segments is retarded. The network model of the stereocomplex, and the possibility of the formation of a double helix are discussed.

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Zusammenfassung Stereokomplexe von isotaktischem (i) und syndiotaktischem (s) Polymethylmethacrylat (PMMA), mit verschiedener Stereoregularität ders-PMMA Komponente, in C₆D₆ und CD₃CN Lösung, wurden durch¹H NMR Spektra mit Magisch-Winkel-Rotation (MAR-NMR), durch Breitband (BL) NMR Spektra und durch¹³C NMR Spektra mit starker Protonenentkopplung untersucht. Es wurde herausgefunden, daß in assoziierten Segmenten des Stereokomplexes mitp = 30–40% (p ist der Bruchteil der assoziierten Monomereinheiten) die-CH³ und CH²-Gruppen die gleiche Beweglichkeit wie in Lösungen von nur s oder nuri-PMMA ausweisen, aber infolge der Wechselwirkung der Estergruppen sind diese Bewegungen raumbehindert. In Komplexen mit einem hohen Grad von Wechselwirkungen (p 75%) ist die Beweglichkeit der-CH³ und CH²-Gruppen in assoziierten Segmenten verzögert. Das Netzwerkmodell des Stereokomplexes, sowohl als auch die Möglichkeit einer Doppelhelixform, werden diskutiert.

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Dedicated to Prof. Dr. G. Rehage on the occasion of his 60th birthday.

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With 2 figures and 1 table