15 Fakultätsübergreifend / Sonstige Einrichtung
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Item Open Access Electronic properties of the triplet state of fluorene, carbazole, dibenzofuran and dibenzothiophene(X-traps)(1979) Goldacker, Wilfried; Schweitzer, Dieter; Zimmermann, HerbertThe triplet state of X-traps in neat single crystals of fluorene, carbazole, dibenzofuran and dibenzothiophene was investigated bv the method of ODMR in zero field at 1.3 K. In addition to the intersystem crossing rates, steady state populations, decay rate constants and relative radiative rate constants of the sublevels, the spin-lattice relaxation (SLR)-rates were measured, which could not be neglected even at this low temperature. In the case of dibenzothiophene a strong intramolecular heavy-atom effect due to the sulphur atom was observed which allowed direct So → T1 excitation.Item Open Access Resonance and relaxation attenuation by neutral acceptors in a magnetic field(1977) Schad, Hanspeter; Lassmann, Kurt; Zeile, HeinrichFine structure, level splitting, and relaxation times of the acceptor ground state in cubic semiconductors can be deduced from ultrasonic attenuation. By the application of a magnetic field it is possible to vary the coupling strength and the number of acceptors on speaking terms with the ultrasonic wave. Making use of this possibility, we have determined directly effective coupling constants for relaxation attenuation and the temperature dependence of the critical intensity for saturation of the resonant interaction. Results obtained for p-type GaAs and Si are discussed in comparison with analogous results for glasses.Item Open Access Vibration analysis and deformation measurement(1978) Tiziani, Hans J.It appears that speckle techniques for deformation measurement and vibration analysis will be developed further. The results obtained are generally easy to interpret, compared with those from holographic interferometry, and the mathematics involved is not difficult. Finally, the equipment necessary for laser speckle photography is not unduly complicated.Item Open Access Transanular interaction in [2.2]phanes: models for dimers?(1979) Goldacker, Wilfried; Hausser, Karl H.; Schweitzer, Dieter; Staab, Heinz A.The emission spectra of pseudo-ortho 3 and pseudo-geminal-4,7,12,15-tetramethoxy[2.2]-paracyclophane 3 were measured in glass matrices at 1.3 K. Furthermore, the zero field splitting parameters D and E and the decay rate constants ki of the excited triplet state were studied by optical detection of magnetic resonance in zero field. The results were compared with the corresponding monomer 1,4-dimethyl-2,5-dimethoxybenzene.Item Open Access Investigation of the excited triplet states of [2.2]- and [3.3]paracyclophane(1979) Melzer, Guenter; Schweitzer, Dieter; Hausser, Karl H.; Colpa, Johannes Pieter; Haenel, MatthiasWe have studied the excited triplet states of [2-2]- and [3.3]paracyclophane by emission spectroscopy and by ODMR and have compared the results with the corresponding monomer paraxylene. The most striking result is that both phanes exhibit two sets of zero field splitting parameters indicating the existence of two nearly degenerate low lying excited triplet states. Furthermore, we find in distinction to expection a stronger reduction of the zero field splitting parameters as compared to the monomers for [3.3]paracyclophane than for [2.2]paracyclophane. The causes of these surprising experimental findings are discussed.Item Open Access Beurteilung der Bildqualität von Luftbildkammern(1977) Tiziani, Hans J.La fonction de transfert optique (OTF) se révèle un moyen très précieux pour comparer et se rendre compte de la qualité des systèmes optiques. 0n peut meme tenir compte des facteurs de l'environnement, tels que le mouvement des avions et de l'influence de l'atmosphère sur la qualité d'image. Les valeurs mesurées péuvent etre comparées aux valeurs calculées á partir des caractéristiques des lentilles. A l'aide d'un modèle basé sur des experiences, il fut possible d'établir une courbe de la valeur des seuils. Elle permet une comparaison entre les resultats basés sur la fonction de transfer de modulation et les resultats obtenus par des tests habitueIs de mesure du puvoir séparateur. Actuellement nous cherchons à réduire le volume des données provenant de calculs et de mesures, pour établire des indices de qualité et de focalisation utilisables en pratique.Item Open Access ODMR of phanes and charge transfer phanes(1979) Schweitzer, Dieter; Goldacker, Wilfried; Hausser, Karl H.; Staab, Heinz A.Triplet zero field splitted parameters |D| and |E| and decay rates ki of the triplet sublevels of two stereoisomeric tetramethoxy [2.2] paracyclophanes as well as those of two CT [2.2] paracyclophanes in low concentration in glasses and small neat single ctystals as measured by ODMR in zero fields at 1,3 K are presented.Item Open Access The use of optical transfer function for assessing the quality of optical systems(1978) Tiziani, Hans J.The optical transfer function (OTF) has proved to be a highly valuable aid in comparing and evaluating the quality of optical systems. The measuring instrument developed is briefly described. The OTF measurements agreed well with theoretical results obtained from lens data, especially for the modulation transfer function (MTF). With the aid of a model based on experiments, a threshold curve was obtained which enabled the results based on the MTF to be compared with those from conventional resolution tests. To enable workable focusing and quality criteria to be derived, an attempt was made to condense the profuse data resulting from the MTF.Item Open Access Molecular structure and spectroscopic properties of Kekulene(1979) Krieger, Claus; Diederich, Francois; Schweitzer, Dieter; Staab, Heinz A.Considerable bond localization has been detected in kekulene(1) by X-ray structure analysis: only every second ring is "aromatic". This initially surprising result is in accord with various spectroscopic properties of (1).Item Open Access Transanular interactions in [2.2]phanes-relation between spectroscopic properties and structural parameters of [2.2]phanes(1978) Colpa, Johannes Pieter; Hausser, Karl H.; Schweitzer, DieterIn this paper we attempt to explain the spectroscopic properties of a number of [2.2]phanes. All phanes discussed have in common that their two subunit.