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Item Open Access Emission, absorption and propagation of acoustic THz-waves in solids(1979) Eisenmenger, WolfgangRecent experimental developments in generation and detection of THz acoustical phonons have led to studies of phonon emission, propagation and absorption in solids. New results of this acoustical phonon spectroscopy concern phonon interactions with collective excitations (phonons, photons, magnons), localized excitations (resonant scattering of impurities, radiationless transitions) and electronic excitations in metals, superconductors and semiconductors. The different experimental methods and their applications to phonon interaction studies are discussed.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 Measurements of effective quasiparticle recombination times and of densities of electronic states at the Fermi level in superconducting Al- and Pb-films(1979) Epperlein, Peter W.; Eisenmenger, WolfgangTemperature-dependent quasiparticle recombination lifetimes tau exp (T) and densities N 0 of electronic states at the Fermi level have been measured from time decay experiments of excess quasiparticle concentrations in evaporated, superconducting Al- and Pb-tunnel junctions. Current pulses were used to inject excess, nonthermal quasiparticles in a single junction acting simultaneously as generator and detector. The experimental lifetimes in "unperturbed" Al show satisfactory agreement with calculations based on the 2Delta-phonon trapping lifetime model. Tau exp decreases with increasing perturbations of the Al film structure by oxygen background evaporation. In Pb the measured times indicate 2Delta-phonon volume losses. The densities N 0 in Pb-films and "unperturbed" as well as oxygen-perturbed Al-films differ by less than 5% from the corresponding bulk material data. Therefore, in trying to explain the enhancement of the transition temperature from 1.23 K to 1.85 K in perturbed, granular Al-films a change of N 0 can be ruled out.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 Molekülstruktur und spektroskopische Eigenschaften des Kekulens(1979) Krieger, Claus; Diederich, Francois; Schweitzer, Dieter; Staab, Heinz A.Beträchtliche Bindungslokalisation im Kekulen (1) wurde durch Röntgen-Strukturanalyse nachgewiesen: Nur jeder zweite Ring ist "aromatisch". Dieser zunächst überraschende Befund ist mit einigen spektroskopischen Eigenschaften von (1) in Einklang.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 Localization and diffusion of positive muons in metals(1979) Orth, Helmut; Döring, Klaus-Peter; Gladisch, Michael; Herlach, Dierk; Maysenhölder, Waldemar; Metz, Harald; Putlitz, Gisbert zu; Seeger, Alfred; Vetter, J.; Wahl, W.; Wigand, M.; Yagi, EiichiDie Grundeigenschaften positiver Müonen (positive Elementarladung, Spin 1/2, Massenverhältnis Müon/Proton ≈ 1/9, großes magnetisches Moment, paritätsverletzender Zerfall in ein Positron und zwei Neutrinos) und ihre Verfügbarkeit in Form intensiver spinpolarisierter Strahlen in "Mesonen-Fabriken" gestatten es, mit Hilfe der μ+SR ("Müon-Spin-Rotation")-Methode die Wechselwirkung der Müonen mit Magnetfeldern in Metallen zu studieren. In dieser Arbeit geben wir einen kurzen Überblick über die μ+SR-Methode und ihre Anwendung auf das Studium der Lokalisierung und Diffusion von Müonen in Metallen für den Fall der dipolaren Wechselwirkung mit den magnetischen Momenten der Kerne. Die Zusammenhänge zwischen den gemessenen Relaxationsraten und der Müonenbeweglichkeit und dem Einfang und Entweichen an Verunreinigungen werden dargestellt und anhand von Messungen an hochreinen Be-, Nb- und Ta-Einkristallen veranschaulicht.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 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 Einfluß von Fremdionen auf die Elektronenprozesse in Ionenkristallen(1979) Persic, Ja. N.; Gutman, V. I.; Pertschi, Ottmar (Übersetzer)Es wurde festgestellt, daß die additive Verfärbung die elektrischen Eigenschaften der Alkalihalogenidkristalle wegen der in diesen vorkommenden Schwermetallverunreinigungen, deren Ionen Elektroneneinfangzentren sind, beeiflußt. Untersucht wurde der Elektroneneinfang durch Fremdionen in röntgenbestrahlten Kristallen. Es wird ein Kristallverfärbungsverfahren mit flacher Metallkathode beschrieben.