Browsing by Author "Hausser, Karl H."
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Item Open Access Dynamic nuclear polarisation in p-doped silicon by microwave ultrasonics(1969) Hausser, Karl H.; Schweitzer, DieterWe have investigated the dynamic nuclear polarisation (DNP) of 29 Si nuclei in highly doped silicon single crystals. The saturation of the electronic Zeeman levels in a magnetic field of 3.3 kG at 1.6°K was obtained using microwave ultrasonics of about 9 GHz. The ultrasonic waves were generated in a cavity by means of a transducer consisting of a thin film of CdS evaporated on the polished surface of the silicon. Preliminary results obtained with a silicon-rod of 2 x 2 x 12 mm cut with the long axis parallel to the (110) direction rendered a reduction of the NMR signal to about ⅓ in agreement with the expected negative sign of the DNP.Item Open Access Electron spin echo determination of spin diffusion in the one-dimensional conductor (fluoranthenyl)2+(PF6)x-(SbF6)1-x-(x ≈ 0.5)(1983) Sigg, Jakob; Prisner, Thomas; Dinse, Klaus Peter; Brunner, Hermann; Schweitzer, Dieter; Hausser, Karl H.-Item Open Access Electron-spin-echo experiments on the one-dimensional conductor [(fluoranthene)2]+[(PF6)x(SbF6)1-x]- (x≈0.5)(1983) Sigg, Jakob; Prisner, Thomas; Dinse, Klaus Peter; Brunner, Hermann; Schweitzer, Dieter; Hausser, Karl H.The electron-spin-echo decay function was determined for the conducting phase of [(C16H10)2]+X- in the temperature range 183-300 K. The decay function exhibited an exp[-(γt)3/2] dependence, characteristic of one-dimensional spin diffusion. The ratio 5×106≤D∥/D⊥≤5×108 for the inner-stack-to-out-of-stack diffusion rates was determined from the characteristic time t0, at which the electron-spin-echo decay function changed to the "conventional" exp(-2γ′τ)) form. The deduced value 2×1013≤D∥≤2×1016 rad/s is consistent with the bulk dc conductivity and with recently determined nuclear spin-lattice relaxation rates. The overall assumption of highly mobile electronic spins was confirmed by an Overhauser-type experiment.Item Open Access Electronic properties of kekulene(1982) Schweitzer, Dieter; Hausser, Karl H.; Vogler, Helmut; Diederich, Francois; Staab, Heinz A.The fluorescence and phosphorescence of kekulene in a host matrix of polycrystalline tetrachlorobenzene are investigated, together with the triplet zero field splitting parameters |D| and |E| obtained by ODMR in zero field. The D value is also calculated within a semi-empirical π-theory and compared with experiment. It could be shown that the triplet state energies of a number of different sites of kekulene in the host matrix and the zero field splitting parameters are related, in first order, by spin orbit interaction.Item Open Access Electronic properties of two isomeric charge transfer [2.2]paracyclophanes(1976) Schweitzer, Dieter; Hausser, Karl H.; Taglieber, Volker; Staab, Heinz A.The emission spectra and the zero field splitting parameters of the two diastereomeric 4,7-dicyano-12,15-dimethoxy-[2.2] paracyclophanes 3 and 4 in comparison to the corresponding monomers 1 and 2 were investigated in order to study the orientation dependence of charge transfer (CT) interactions. The general results in glasses (PMMA) are: broad structureless emission bands with large spectral overlap between fluorescence and phosphorescence; strong reduction of the zero field splitting parameters D and D* by a factor of two for the pseudo-ortho isomer 3 and by a factor of four for the pseudo-geminal isomer 4 showing the strong effect of the geometrical orientation. In single crystals of the same phanes the zero field parameters were found to be further reduced to about one fifth of the value of the monomers which indicates, in accordance with the emission spectra, an additional intermolecular interaction between adjacent phanes.Item Open Access Electronic spectra and triplet state properties of superphane(1986) Schweitzer, Dieter; Hausser, Karl H.; Vogler, Helmut; Staab, Heinz A.; Boekelheide, VirgilThe emission and the zero-field splitting parameters D and E of the superphane 1 and the [25](1,2,3,4,5)-cyclophane 2 are investigated. The large number of six and five methylene bridges, respectively, leads to a more rigid molecular frame and to a smaller transanular distance as compared to other [2.2]cyclophanes. The experimental results exhibit characteristics features which are due to these unusual properties; they are discussed and compared with semi-empirical Π-electron calculations.Item Open Access Influence of an identified dimer vibration on the emission spectrum of [2,2]paracyclophane(1980) Goldacker, Wilfried; Schweitzer, Dieter; Dinse, Klaus Peter; Hausser, Karl H.The emission spectrum of polycrystalline [2,2]paracylophane shows a resolved vibronic structure with a 241 cm−1 progression at He temperatures. The dependence of the energy of this mode upon selective deuteration in combination with results from FIR and Raman spectra could be used to identify the mode as a torsional dimer vibration. The emission spectra could be simulated assuming a linear coupling of the torsional mode to the electronic transitions with coupling strengths of S = 10 (fluorescence) and S = 13 (phosphorescence). This corresponds to an equilibrium displacement of the benzene rings under electronic excitation by a torsional angle of 10.6° (S1) and 12.1° (T1), in addition to the small torsion in the ground state S0 by about 3°.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 ODMR of triplet states of organic electron donors(1986) Grimm, Hans; Schweitzer, Dieter; Hausser, Karl H.; Keller, Heimo J.Energies of the first excited triplet states and triplet zero field splitting parameters /D/ and /E/ of several organic donors - usually used for the preparation of organic metals and superconductors - are reported.Item Open Access Optical detection of magnetic resonance (ODMR) of naphthalenophanes(1981) Schweitzer, Dieter; Hausser, Karl H.; Blank, Norman E.; Haenel, Matthias-Item Open Access Optical detection of magnetic resonance (ODMR) of triple-layered phanes(1981) Melzer, Guenter; Schweitzer, Dieter; Hausser, Karl H.; Staab, Heinz A.; Zapf, Udo-Item Open Access Overhauser effect experiments on the one-dimensional conductor (perylene)2+PF6-·2/3THF(1984) Brunner, Hermann; Hausser, Karl H.; Keller, Heimo J.; Schweitzer, DieterWe have measured the Overhauser enhancement of the protons and the 19F-nuclei of the one-dimensional conductor (perylene)2+PF6-·2/3THF in its metallic phase at room temperature. The enhancement factor V was found to be VP=+320±20 for the protons and VF=+175±40 for the 19F-nuclei indicating a predominantly scalar interaction with the conduction electrons in both cases.Item Open Access Spectroscopic properties of kekulene(1981) Schweitzer, Dieter; Hausser, Karl H.; Diederich, Francois; Staab, Heinz A.; Vogler, HelmutKekulene [1,2] is the first example of a new class of aromatic compounds in which the annelation of six membered rings leads to a cyclic system enclosing a cavity with hydrogen atoms.Item Open Access Spin rotation interaction and anisotropic chemical shift in 13CS2(1971) Spiess, Hans Wolfgang; Schweitzer, Dieter; Haeberlen, Ulrich; Hausser, Karl H.The 13C nuclear spin-lattice relaxation time T1 was studied in liquid CS2 from -106°C to +35°C at resonance frequencies of 14, 30, and 62 MHz. The relaxation is caused by anisotropic chemical shift and spin-rotation interaction. It is shown that for linear molecules the spin-rotation constant C and the anisotropy of the chemical shift Δσ can be obtained from the relaxation rates without use of adjustable parameters. The analysis yields: C = -13.8 ± 1.4 kHz and Δσ = 438 ± 44 ppm.Item Open Access Transannular interactions in [2.2] phanes as studied by luminescence and optical detection of magnetic resonance(1976) Schweitzer, Dieter; Colpa, Johannes Pieter; Hausser, Karl H.; Haenel, Matthias; Staab, Heinz A.Emission spectra of different types of [2.2] naphthalenophanes were measured at 1.25 K in glasses as well as in small single crystals. In addition, the D and E values of the excited triplet states were studied by optical detection of magnetic resonance in zero field and the results compared with the corresponding monomeres.Item Open Access Transannular interactions in [2.2] phanes as studied by magnetic resonance and optical spectra(1975) Schweitzer, Dieter; Colpa, Johannes Pieter; Behnke, J.; Hausser, Karl H.; Haenel, Matthias; Staab, Heinz A.The interaction of π-electrons in [2.2] phanes was studied both experimentally and theoretically. The fluorescence and phosphorescence spectra were measured at liquid helium temperature; in addition, the zero field splitting parameters D and E were determined by ODMR in zero field and by ordinary ESR at X-band. The results for the phanes with two identical aromatic units can be summarized as follows: The rather small reduction of the D and E values of the order of 10% with respect to the monomers indicates, in agreement with the theoretical treatment given in part II, that the two unpaired electrons of the excited triplet state have a high probability to be at a given time in the same half of the molecule. While the fluorescence spectra show the typical behaviour of emission spectra of dimers or excimers, the phosphorescence spectra exhibit some remaining structure. This behaviour which indicates a somewhat weaker coupling among the triplet orbitals as compared to the singlet orbitals can also be understood on the basis of theoretical considerations. For a phane with two different aromatic units the behaviour is found to be more similar to the corresponding aromatic monomer with the lower excited states with some perturbation by the other part of the phase also in agreement with theoretical expectation.Item Open Access Transanular interaction in [2.2]phanes: [2.2](2,7)pyrenophane(1976) Schweitzer, Dieter; Hausser, Karl H.; Kirrstetter, Reiner G. H.; Staab, Heinz A.The emission spectra of [2.2](2,7)pyrenophane and the zero field splitting parameters D and E of its excited triplet state were measured in glasses and in small single crystals at 1.3 K. The results are being compared with monomer pyrene and 2,7 dimethylpyrene in liquid and solid solutions as well as in single crystals.Item Open Access Transanular interaction in [2.2]phanes: [2.2](4,4')diphenylophane and [2.2](2,7) fluorenophane(1978) Schweitzer, Dieter; Hausser, Karl H.; Haenel, MatthiasThe emission spectra and the zero field splitting parameters D and E of the first excited triplet states of [2.2](4,4′) diphenylophane 3 and of the two stereoisomeric syn- and anti [2.2] (2,7) fluorenophanes 4a and 4b are investigated and compared with those of the corresponding monomers.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.