Showing papers in "Zeitschrift für Naturforschung A in 1994"
TL;DR: In this article, the set-up of a molecular beam Fourier transform microwave spectrometer in the range from 26.6 to 40 GHz was presented, which can be used to measure highly resolved rotational spectra of van der Waals complexes.
Abstract: We present the set-up of a molecular beam Fourier transform microwave spectrometer in the range from 26.6 to 40 GHz. As a test we investigated the deuterium hyperfine structure of deuteroacetonitrile, DCH 2 CN. It is also shown, that the spectrometer can be used to measure highly resolved rotational spectra of van der Waals complexes
45 citations
TL;DR: A series of trichlorogermanate (II) salts (AGeCl 3, A = Rb, Cs, CH 3 NH 3, and (CH 3 ) 4 N) have been synthesized and characterized by 35 Cl NQR, 35 CL NMR, AC conductivity, DTA, and X-ray diffraction techniques.
Abstract: A series of trichlorogermanate (II) salts (AGeCl 3 , A = Rb, Cs, CH 3 NH 3 , and (CH 3 ) 4 N) have been synthesized and characterized by 35 Cl NQR, 35 Cl NMR, AC conductivity, DTA, and X-ray diffraction techniques. In the temperature range studied two, two, five, and four phases were confirmed for the Rb, Cs, CH 3 NH 3 , and (CH 3 ) 4 N salts, respectively. From the 35 Cl NQR and structural data, isolated pyramidal GeCl 3 − anions were recognized in the low temperature phases. With increasing temperature the relaxation times of the 35 Cl NQR decreased exponentially and the signals disappeared far below the melting point. This suggests that the reorientation of the anion about the pseudo three-fold axis is excited
39 citations
TL;DR: In this article, a new highly sensitive 1 H- 14 N nuclear quadrupole double resonance technique is presented which is based on magnetic field cycling and on the application of multiple frequency sweeps of an r.f, magnetic field.
Abstract: A new highly sensitive 1 H- 14 N nuclear quadrupole double resonance technique is presented which is based on magnetic field cycling and on the application of multiple frequency sweeps of an r.f, magnetic field. The sensitivity and the resolution of the new technique are estimated. Some experimental results obtained by the new technique are presented
35 citations
TL;DR: In this paper, the effect of temperature on absorption and fluorescence of 1-phenyl-4- diphenylthiophosphinyl butadiene (PDPB) and of the direct irradiation on the absorbance were investigated in polyvinyl alcohol (PVA) film.
Abstract: The effect of temperature (from 296 to 423 K) upon the absorption and fluorescence of 1-phenyl-4- diphenylthiophosphinyl butadiene (PDPB) and of the direct irradiation on the absorbance were investigated in poly(vinyl alcohol) film. It was found that for PDPB in PVA film the transition from cis to trans configuration is only possible as a result of thermal isomerization due to the softening of PVA polymer, whereas photoisomerization results in both cis-to-trans and trans-to-is transitions. Similar as with 1,4-diphenyl-1,3-butadiene in PVA, the luminescence is due to two, trans-trans and cis-trans, PDPB conformers
30 citations
TL;DR: In this paper, an object-oriented programming environment for numerical simulation of magnetic resonance spectra is introduced and applied to NQR and NMR of quadrupolar nuclei using a Floquet approach.
Abstract: An object-oriented programming environment for numerical simulation of magnetic resonance spectra is introduced and applied to NQR and NMR of quadrupolar nuclei. Using a Floquet approach it is possible to perform simulations of spin systems that are described by explicitly time-dependent Hamiltonians in full analogy to simulations of time-independent systems. Applications to magic angle spinning and double rotation are discussed
28 citations
TL;DR: In this article, the authors performed dielectric relaxation studies of 4-n-octyl-4'-cyanobiphenyl (8 CB) in the pressure range 0.1-120 MPa, the frequency range 1 kHz-13 MHz and the temperature range 295-331 K.
Abstract: Dielectric relaxation studies of 4-n-octyl-4'-cyanobiphenyl (8 CB) were performed in the pressure range 0.1-120 MPa, the frequency range 1 kHz-13 MHz and the temperature range 295-331 K. The dielectric behaviour of 8 CB in the nematic phase is similar to that of 5 CB, 6 CB and 7 CB. In particular, the activation enthalpy decreases with increasing pressure and the activation volume decreases with increasing temperature in the nematic phase. In the smectic A phase of 8 CB both these parameters are markedly lower and show opposite pressure and temperature dependencies. We tentatively interpret these effects as a result of breaking of the dipole-dipole correlations which manifests itself differently in these liquid crystalline phases
24 citations
TL;DR: In this article, the influence of the ammonium ion dynamics on the structural stability of these crystals was discussed with special regard to the influence on the chemical properties of ammonium-ion dynamics.
Abstract: Recent and novel data obtained from chlorine NQR measurements on natural and deuterated (NH 4 ) 2 MCl 6 compounds are discussed with special regard to the influence of the ammonium-ion dynamics on the structural stability of these crystals. The temperature dependence (4.2 K to 350 K) of the chlorine NQR frequency ν Q and relaxation rates T 1 −1 , T 2 −1 obtained from the natural ammonium salts of Sn, Pd, Os, Pb, Te, Se and from the deuterated salts of Sn, Te and Se are analysed. Slight deviations from the normal temperature behaviour of ν Q and T 1 −1 are found in Sn, Pd and Os compounds which stay cubic in the whole temperature range. The ammonium compounds of Pb and Te undergo a structural transformation between 80 K and 90 K from the cubic to a trigonal phase which is distinguished by the preservation of the single line spectrum of the chlorine NQR below T c1
22 citations
TL;DR: In this paper, the power of solid state NMR to characterise solids by determining the nuclear quadrupole coupling of the constituent nuclei is demonstrated for a number of compounds of current interest in a materials science laboratory.
Abstract: The power of solid state NMR to characterise solids by determining the nuclear quadrupole coupling of the constituent nuclei is demonstrated for a number of compounds of current interest in a materials science laboratory. Recent results are presented for the nuclei 17 O, 23 Na, 27 Al, 39 K, 71 Ga, 91 Zr, 93 Nb, and 139 La. These were derived using a variety of FT NMR techniques including static, magic angle spinning and frequency stepped spin echo NMR spectroscopy
21 citations
TL;DR: In this paper, the authors present experimental results on stabilizing unstable periodic orbits of an autonomous chaos oscillator based on a simple electronic circuit, which is achieved by applying the difference between the actual and a delayed output signal of the oscillator.
Abstract: We present experimental results on stabilizing unstable periodic orbits of an autonomous chaos oscillator based on a simple electronic circuit. Control is achieved by applying the difference between the actual and a delayed output signal of the oscillator. The quality of chaos control can be measured via the strength of perturbation. The dependence on the delay time shows a characteristic resonancetype behavior.
20 citations
TL;DR: In this paper, the splittings observed in the 209 Bi nuclear quadrupole resonances of α-Bi 2 O 3, in zero magnetic field, follow the typical pattern of a Zeeman perturbed NQR spectrum.
Abstract: The splittings observed in the 209 Bi nuclear quadrupole resonances of α-Bi 2 O 3 , in zero magnetic field, follow the typical pattern of a Zeeman perturbed NQR spectrum. The lineshapes in Bi 3 O 4 Br also indicate a poorly resolved splitting that points to the presence of an internal magnetic field in the order of 200 G. This exceeds notably the dipole nuclear magnetic fields (about several G), but is orders of magnitude smaller than paramagnetic fields produced by unpaired electron spins. The results obtained using a SQUID and μSR-technique can also be interpreted as indicative of magnetic properties not conventionally expected in such compounds
19 citations
TL;DR: In this paper, an alternative reconstruction method of nutation spectra is suggested making use of the Hankel Transform, in which the nutation lineshape is a superposition of spectra from the randomly oriented single crystals.
Abstract: In single crystals the NQR nutation frequency depends on the relative orientation of the coil and the quadrupole axes. In powders the nutation lineshape is a superposition of spectra from the randomly oriented single crystals, so that powder patterns appear in such experiments if the reconstruction is performed by the Fourier transform method. An alternative reconstruction method of nutation spectra is suggested making use of the Hankel Transform. In this way the nutation spectra are simplified. Singularities arising with experiments for the determination of the asymmetry parameter η can easily be resolved. In the particular case of an axially symmetric quadrupolar tensor and a homogeneous radiofrequency field one can reduce the powder pattern to a single line without heterogeneous broadening with respect to orientation
TL;DR: In this paper, the structural assignment of Ca NMR lines measured in 43 Ca-enriched samples or n = 2 ((Bi, Pb),Sr 2 CaCu 2 O 8+x ) and n = n = 3 ((Bi and Pb) 2 Sr 2 Ca 2 Cu 3 O 10+x ).
Abstract: As a first step or a study or the electronic properties or CuO 2 planes by probing calcium nuclei in the bismuth-based high-T c materials we report here the structural assignment of Ca NMR lines measured in 43 Ca-enriched samples or n = 2 ((Bi, Pb),Sr 2 CaCu 2 O 8+x ) and n = n = 3 ((Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10+x ) bismuth compounds. Powdered samples were investigated as well as oriented powders, achieved by uniaxial alignment or the grains in a 7 T magnetic field. For the main calcium site (Ca between two CuO 2 planes), we could determine the quadrupolar as well as the shirt tensors. The results indicate that, in the same way as yttrium nuclei in YBaCuO, calcium nuclei are sensitive to the magnetic susceptibility or the metallic CuO 2 planes
TL;DR: In this article, a new derivation of the Maxwell-Dirac isomorphism is presented and a complete set of transformations connecting Maxwell's electrodynamics and wave mechanics is obtained.
Abstract: Abstract A new derivation of the Maxwell-Dirac isomorphism is presented. A complete set of transformations connecting Maxwell's electrodynamics and wave mechanics is obtained.
TL;DR: In this article, the short range structure of molten ErCl 3 at 1053 K was investigated by X-ray diffraction, and the coordination number of ErCl 6 3- octahedra was estimated.
Abstract: The short range structure of molten ErCl 3 at 1053 K was investigated by X-ray diffraction. The nearest neighbour distance of Er 3+ -Cl − and the coordination number of Cl − around Er 3+ were estimated to be 2.63 A and 5.8 A, respectively, and the Er 3+ -Er 3+ and Cl − -Cl − distances 4.05 A and 3.75 A, respectively. The ratio of the anion-anion pair distance to the cation-anion pair distance (r −− /r +− ) was, therefore, 1.43, being close to 1.41, characteristic of octahedral geometry. These results indicate that ErCl 6 3- octahedra exist in molten ErCl 3 . Probably Er 2 Cl 10 4- and a small amount of Er 2 Cl 11 5- ions are formed according to the geometrical calculations of bond lengths and bond angles
TL;DR: In this paper, the nuclear quadrupole coupling constants for D, 14 N and 17 O with basis sets of high local quality were reviewed and it was confirmed that this concept gives reliable results for many molecules in the gas phase.
Abstract: Nuclear quadrupole coupling constants for D, 14 N and 17 O calculated with basis sets of high local quality are reviewed. It is confirmed that the concept of high local quality gives reliable results for many molecules in the gas phase. The calculations are extended to the condensed phase by combining quantum chemical calculations with molecular dynamics simulations. An excellent agreement with experiment is obtained for the deuterium coupling in liquid D 2 O and a fair agreement for 17 O coupling in liquid H 2 17 O. The 21 Ne nmr relaxation time in liquid neon is calculated to be within about 20% of experimental values, an exact comparison being difficult due to only roughly known pressures in the experiment and not adequately treated quantum effects in the simulations. Comparisons in the dense supercritical region at higher temperatures would be of interest, but experimental data are lacking
TL;DR: In this paper, the 79,81 Br NQR spectra of tetraanilinium decabromotricadmate and 4-methylpyridinium tribromocadmate were studied as function of temperature and their crystal structures were determined.
Abstract: The 79,81 Br NQR spectra of tetraanilinium decabromotricadmate (1) and 4-methylpyridinium tribromocadmate (2) were studied as function of temperature and their crystal structures were determined. (C 6 H 5 NH 3 ) 4 Cd 3 Br 10 (1): Space group D 2h 15 − Pbca, Z = 4, a = 2507.8(7) pm, b = 1995.4(5) pm, c = 763.0(2) pm. Characteristic for the structure are trioctahedral units [Cd 3 Br 10 ] condensed to planes. Within the units the octahedra are face connected and further condensed to planes via common corners. Two types of hydrogen bonds are observed. The 81 Br NQR lines with frequencies (MHz, 298 K) of 62.98, 52.59, 43.39, 41.82, and 40.71 are little temperature dependent with positive and negative coefficients. The wide frequency range of the NQR lines is reflected by the wide range of the intraionic distances, 263 ≤ d(Br − Cd)/pm ≤ 300
TL;DR: In this article, the β spectrum of a mass-separated thin 35S source has been measured with a small-volume Si photodiode and an upper limit of 0.59% (95% CL) was determined.
Abstract: Abstract The β spectrum of a mass-separated thin 35S source has been measured with a small-volume Si photodiode. The energy-dependent response function of the total experimental set-up was calculated by the Monte Carlo method without any adjustable parameter. For an admixture of the hypothetical 17 keV neutrino, an upper limit of 0.59% (95% CL) was determined. Neglecting electron scattering on the spectrometer diaphragm was shown to generate a false 17 keV neutrino admixture of 0.3%.
TL;DR: In this paper, a definition for the number of electrons χ involved in a three-center bond, based upon the corresponding two-center index indices, was proposed. But it is not shown that χ does not depend on χ.
Abstract: A definition is proposed for the number of electrons χ involved in a three-center bond, based upon the corresponding two-center bond indices. The number of electrons is fractionary, ranging from about 1 to somewhat more than 4 in the systems considered here. It is seen that the sign of the three-center index does not depend on χ
TL;DR: In this paper, it was shown that the individual signs of the off-diagonal elements of the nuclear quadrupole coupling tensor can not be determined from the rotational spectrum of only one isotopomer.
Abstract: If off-diagonal elements of the nuclear quadrupole coupling tensor are determined from the rotational spectrum of only one isotopomer, the magnitude of the off-diagonal elements and the sign of the product χ ab x bc x ac can be obtained but not the individual signs of the off-diagonal elements. In this article we give two proofs for this fact. A determination of the individual signs of the off-diagonal elements is only possible by analysing the spectra of more isotopomers
TL;DR: In this paper, the formation of neutral bimolecular clusters of unsubstituted nucleobases and mononucleosides in the gas phase has been studied by IR laser desorption of the neutral molecules into a supersonic beam expansion.
Abstract: The formation of neutral bimolecular clusters of unsubstituted nucleobases and mononucleosides in the gas phase has been studied by IR laser desorption of the neutral molecules into a supersonic beam expansion. The complementary nucleobase pairs adenine-thymine and cytosine-guanine of DNA have been found to be formed in preferenoe to non complementary base pairs. Association constants for the formation of the dimers of free nucleobases and nucleosides in the gas phase are calculated from the experimental results. A strong influence due to side groups affecting the dimer formation of the nucleobases is shown
TL;DR: In this article, the exponential growth of continuous six fold hexagonal order across the isotropic-smectic F phase transition is estimated from the density studies with an exponent b = 0.75
Abstract: The compound N(p-n-decyloxy benzylidene)p-n-tetradecyl aniline, (10O.14), a higher homologue of the MBBA series, exhibits smectic F and smectic G phases. Dilatometric studies inferred strong pre-transitional effects in a large temperature range. DSC results confirmed the first order nature of the IF and FG transitions. The exponential growth of continuous six fold hexagonal order across the isotropic-smectic F phase transition is estimated from the density studies with an exponent b = 0.75
TL;DR: In this paper, the effects of the basis set in these calculations are considered, and the limitations imposed by the nature of the calculation are described, and these are compared with experimental quadrupole coupling parameters.
Abstract: Ab initio SCF calculations were performed in the unit cell environment, making use of the periodic behaviour to compute a wave-function for the bulk material. Electric field gradient (EFG) calculations were performed on the resulting wave-functions, and these are compared with experimental quadrupole coupling parameters. Examples of inorganic molecular and ionic crystals (nitrogen, chlorine and lithium nitride) and minerals or partially covalent lattice structures (alumina, petalite, a-quartz, boron oxide, boron nitride and sulphur nitride) are described. The effects of the basis set in these calculations are considered, and the limitations imposed by the nature of the calculation are described
TL;DR: The spin-lattice relaxation time of 39 K NMR observed in the low-temperature phase (T < 264.1 K) of KNO 2 is explained by the quadrupole mechanism contributed from a newly found NO 2 − motion.
Abstract: The spin-lattice relaxation time of 39 K NMR observed in the low-temperature phase (T < 264.1 K) of KNO 2 is explained by the quadrupole mechanism contributed from a newly found NO 2 − motion. The in-plane C 3 reorientation and the overvall NO 2 − rotation as well as the self-diffusion were shown in the intermediate phase (T ≤ 314.7 K) and the high-temperature plastic phase (T < melting point: 710 K), respectively, by observing 39 K and 15 N NMR relaxation times and 15 N lineshapes
TL;DR: In this paper, it was shown that the values which the Wiener numbers of isomeric polyphenyls may assume are all congruent modulo 36 are all true.
Abstract: Abstract It is shown that the values which the Wiener numbers of isomeric polyphenyls may assume are all congruent modulo 36. Similarly, the Wiener numbers of isomeric phenylens are always congruent modulo 18. These findings provide a rationalization for the known fact that the isomer-discriminating power of the Wiener number is rather weak. Extensions of the present results to more general classes of graphs are also pointed out.
TL;DR: In this paper, the authors use the BZ-reaction and the MBO-response to implement the Boolean functions AND, OR, NAND, and NOR by the coupling of three chemical reactors.
Abstract: Abstract We use the BZ-reaction and the MBO-reaction to implement the Boolean functions AND, OR, NAND , and NOR by the coupling of three chemical reactors. The experimental setup is analogous to a simple neural feedforward network with two reactors serving as the input layer and one reactor as the output layer. Coupling between the input and output reactors is carried out through the flow rate (BZ- and MBO-reaction) and through the electrical current by the use of Pt working electrodes (BZ-reaction). The XOR- and XN OR functions may be realized with 5 reactors using combinations of the AND, NOR, NOR - and the AND, NOR, Or-chemical gates, respectively.
TL;DR: In this paper, the formation of polycrystalline sodalite from a ternary mixture of mullite, cristobalite and corundum has been investigated.
Abstract: Abstract The hydrothermal formation of sodium hydroxyborate enclathrated sodalite synthesized from an initial ternary mixture of mullite, cristobalite and corundum has been investigated. Depending on temperature and pressure the compound Na7.5[AlSiO4]6[B(OH)4]1.5 · 2H2O could be synthesized in form of polycrystalline powder as well as in form of single crystals. The kinetics of the sodalite growth could be determined at 423 K and 473 K. 29Si-and 27Al MAS NMR was shown to be the preferred method to describe the conversion into sodalite quantitatively. Evidence for the first formation of polycrystalline sodalite has been found after the total dissolution of mullite and cristobalite. Single crystal X-ray diffraction data were used for the structure determination and refinement. The position and orientation of the hydroxyborate anions within the sodalite's /β-cages could only be found in the course of a \"rigid body\" refinement with constraints for the B(OH)4 tetrahedron. The boron atoms are located in an off-centre position within the sodalite cages. One out of the four oxygen atoms of the hydroxyborate group is positioned near the centre of a face of the sodium tetrahedron, whereas the three remaining oxygen atoms are near to the middle of its edges.
TL;DR: In this paper, a proton NMR method is described which enables rotational flow and viscosity measurements of low molecular weight ciphenyl (NLCs) with positive diamagnetic anisotropy.
Abstract: Abstract A proton NMR method is described which enables rotational flow and viscosity measurements of low molecular weight ṉematic ḻiquid c̱rystals (NLC's). This is achieved by an extension of the common NMR field-cycling technique, namely by fast electronic switching of both the external magnetic field direction and strength. In thermodynamic equilibrium, the director of an NLC with positive diamagnetic anisotropy (Δχ > 0) orients parallel to the external magnetic field. Thus a change of this direction causes a reorientation process of the molecules to align to the new equilibrium, which in low viscous systems in contrast to polymer liquid crystals is rather fast and hence requires fast field switching. We have studied systematically this response as a function of the initial field rotation angle 90 relative to the director for some homologous NLC's of the n-alkyl-cyano-biphenyl (nCB) series. It is shown that there exists a critical angle θcr in such a way that for θo < θcr, however (e.g. in the case of 5 CB θcr is ≈ 85 degrees) the viscoelastic behaviour is more complicated because of a coupling between flow and director gradients. The analysis of the alignment process by the changes of the proton line spectra also allows to determine the Leslie viscosities α1, α2, α3, α4 + α5, and the average Frank elastic constant K̄ by a single measurement.
TL;DR: In this article, the method of classical trajectories is applied for a double Morse potential modeling indirect reactive collisions of three collinear atoms, and the system shows chaotic scattering, which is studied in details through a hierarchic analysis of the singularities of the time delay function.
Abstract: Abstract The method of classical trajectories is applied for a double Morse potential modeling indirect reactive collisions of three collinear atoms. The system shows chaotic scattering, which is studied in details through a hierarchic analysis of the singularities of the time delay function. Tools of the thermodynamic formalism are used to extract global quantities characterizing the scattering process.
TL;DR: In this paper, an argument based on perturbation theory correlates the isotopic differences with electronic transition moments via vibrational averaging, and the contribution of the second moment isotope effect is especially important.
Abstract: Literature data on H/D isotope effects on polarizability are reviewed. An argument based on perturbation theory correlates the isotopic differences with electronic transition moments via vibrational averaging. The contribution of the second moment isotope effect is especially important. The approach is first illustrated with a calculation on H 2 /D 2 and then employed to correlate differential refractive index data on about twenty other H/D isotopic pairs. A table of bond polarizability isotope effects is presented which permits the estimation of polarizability isotope effects for various kinds of H/D substituted compounds. Coupling these results with known isotope effects on vibrational amplitude permits calculation of vapor phase virial coefficient isotope effects, while combination with refractive index data on liquids yields reasonable values for the sum of the isotope effects on molar volume and electronic second moment
TL;DR: In this article, the mm-wave spectra of 15N18 O and 14N 17 O in both X2 Π1/2 and X 2 Π3/2 states have been measured and assigned for the first time.
Abstract: Abstract The mm-wave spectra of 15N18 O and 14N 17 O in both X2 Π1/2 and X2 Π3/2 states have been measured and assigned for the first time. Improved rotational and, for the first time, 17O hyperfine coupling constants have been derived from the analysis. The 14N17 O data yield parameters of the unpaired electron spatial distribution near both nuclei. Furthermore, the deviation from the Born-Oppenheimer approximation is confirmed on the basis of the rotational constants of five isotopomers. Finally, when comparing the nuclear spin-rotation constants to the ones of other molecules containing 14N or 17O nuclei, a roughly linear proportionality with the rotational constant B is found.