Go toArchive
Browse byFacets
Bookbag ( 0 )
Facet   Publication Year 1992  [X]
Results  642 Items
Sorted by   
Section
Publication Year
1992[X]
101Author    Jan Szczepanski, Robert Pellow, Martin ValaRequires cookie*
 Title    The Kinetics and Formation of Small Carbon Clusters in an Argon Matrix  
 Abstract    Pure carbon clusters, formed by Nd/YAG laser ablation of graphite, have been trapped in an argon matrix at 12 K. The temperature dependence of the prominent infrared absorption bands attributable to C 3 , C 5 , C 6 , and C 9 clusters has been investigated between 12 K and 38 K. The former two are observed to decay and the latter two to grow with increased matrix annealing. A new kinetic model based on solid state diffusion theory and involving thermally activated diffusion and aggregation is introduced. All possible pairwise interactions of the linear carbon clusters from C t to C 10 are included in the model. The coupled differential equations are solved numerically and provide a reasonable fit to the experimental temperature profiles of the known clusters. Predictions emerge from the fit for the unknown matrix infrared frequencies for the C 7 cluster. On the basis of the predicted concentration invariance with temperature for C 7 , the infrared bands at 2128 cm" 1 and 1894 cm" 1 are ascribed to this linear cluster. This attribution supports the recent assignment of the gaseous 2138 cm -1 band to linear C 7 . 
  Reference    Z. Naturforsch. 47a, 595—604 (1992); received November 25 1991 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0595.pdf 
 Identifier    ZNA-1992-47a-0595 
 Volume    47 
102Author    Szilvia Murányi, Zoltän NoszticziusRequires cookie*
 Title    On the Problem of Bromide Control in a Tl 3 + -perturbed Belousov-Zhabotinsky Oscillator  
 Abstract    It is shown that Tl 3+ as a bromide removing perturbant of the BZ oscillators is superior to Ag + in several aspects. A most important advantage is that the upper limit of the actual Br" concentra-tion can be calculated from the potential of a bromide selective electrode in the presence of the corrosive Tl 3+ ions. Experimental Potentiometrie traces of a bromide selective electrode in a Tl 3 + perturbed BZ system show that the Br -concentration stays much below its critical concentration during the oscillations. These observations suggest that free Br" is not the critical intermediate formed during reduction of Ce 4+ and responsible for the negative feedback associated with the oscillations. 
  Reference    Z. Naturforsch. 47a, 605—613 (1992); received January 9 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0605.pdf 
 Identifier    ZNA-1992-47a-0605 
 Volume    47 
103Author    Martin Ystenes, Wolfgang Brockner, Frank MenzelRequires cookie*
 Title    Scaled Quantum Mechanical (SQM) Force Field Calculations of the Hexathiometadiphosphate Anion P 2 SG ~  
 Abstract    By ab initio quantum mechanical calculations on P 2 S^ -its equilibrium energy, geometry and vibrational frequencies along with their PED values have been obtained. The basis sets STO-5G, 6-31G, STO-5G* and 6-31G* were employed, and force field calculations were carried out at the STO-5G and the STO-5G* levels. The calculations show that the assignment for some bands between 180 and 260 cm " 1 should be corrected. Two scaling factors were needed to fit the calculated frequencies with the observed frequencies within a deviation of less then 20 cm " 1 for all vibrations, with the exception of v 6 (B lg). The calculated frequency of this vibration is very dependent on the polarization functions, and use of STO-2G for the 3d-orbitals corrects most of the deviation. STO-5G* and 6-31G* both give a good description of the geometry of the title ion, although STO-5G* yields a 0.04 Ä too short terminal P-S distance. 
  Reference    Z. Naturforsch. 47a, 614—618 (1992); received February 12 1992 
  Published    1992 
  Keywords    Vibrational spectrum, Force field, Thiophosphate, P 2 S£ - 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0614.pdf 
 Identifier    ZNA-1992-47a-0614 
 Volume    47 
104Author    Hans SallhoferRequires cookie*
 Title    Hydrogen in Electrodynamics. VIII The Half-Integer Spin  
 Abstract    After a discussion of the one-component Schrödinger (1926) and the four-component Dirac(1928) representation of hydrogen it is shown that the six-component electrodyamic picture turns out to be considerably simpler and clearer. The computational effort is reduced to a fraction. 
  Reference    Z. Naturforsch. 47a, 619—624 (1992); received December 17 1991 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0619.pdf 
 Identifier    ZNA-1992-47a-0619 
 Volume    47 
105Author    V. I. StepanovRequires cookie*
 Title    Comment on the Osipov-Terentjev Calculation of the Viscosity of Liquid Crystals  
 Abstract    The calculation of the viscosity of liquid crystals based on the rotational diffusion approximation recently reported by Osipov and Terentjev [1 a] is critically examined. It is shown that the main result of their treatment -the evaluation of the activational exponent -arises from the neglect of the second derivative of the distribution function with respect to the azimuthal angle in the Fokker-Planck equation. The correct asymptotic formula for the rotational viscosity coefficient is derived. 
  Reference    Z. Naturforsch. 47a, 625—626 (1992); received August 8 1991 
  Published    1992 
  Keywords    Liquid crystal, Viscosity coefficient, Rotational diffusion, Fokker-Planck equation, Energy barrier 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0625_n.pdf 
 Identifier    ZNA-1992-47a-0625_n 
 Volume    47 
106Author    M. A. Osipov, E. M. TerentjevRequires cookie*
 Title    Reply to the Comment of V. I. Stepanov "On the Osipov-Terentjev Calculation of the Viscosity of Liquid Crystals"  
 Abstract    In his comment on [1], V. J. Stepanov has presented a new expression for the flow-induced correction to the one-particle distribution function in nematic liquid crystals. With the help of this solution he obtained a simple expression for the rotational viscosity y x which does not possess the exponential temperature depen-dence related to the overcoming a potential barrier, contrary to results of [1], From the physical point of view this means that the rotating mesogenic molecule does not overcome the mean field potential barrier but prefers to rotate around the director. We accept the mathematical arguments of the Com-ment and agree that the approximate solution of the stationary Fokker-Planck equation, proposed in [1] (see (2) of the Comment) appears to be incorrect close to singularity point due to the wrong assumption that the last term in the equation can be neglected. At the same time one can not accept the statement of Stepanov that this is a revision of the main result of [1]. In fact, it was shown in [1] that the experimental observed exponential temperature variation of the rotational viscosity of nematics can not be determined by the overcoming of the mean-field potential barrier but is related to the activation-like temperature de-pendence of the "molecular friction" coefficient L This coefficient is the parameter of the mean-field theory, and it was calculated in [1] using the more general correlation function approach. This general 
  Reference    Z. Naturforsch. 47a, 627—628 (1992); received December 19 1991 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0627_n.pdf 
 Identifier    ZNA-1992-47a-0627_n 
 Volume    47 
107Author    H. Schamel, G. HübnerRequires cookie*
 Title    Collisional Isotropisation of a Strongly Magnetized Anisotropic Plasma within the Weak Interaction Approximation  
 Abstract    The equipartition frequency v of an anisotropic plasma is calculated numerically and analytically within the Landau approach for strong magnetic fields and several new integral expressions for v are presented. In the ultra strong magnetic field case, when r c <^b, where r c is the Larmor radius and b the classical distance of closest approach, v is shown to be dependent on how the Coulomb force is cut off at short distances. None of the obtained expressions, however, coincides with experiment, in contrast to the strong interaction theory of O'Neil and Hjorth. For weaker, but still strong magnetic fields (r c >b) the ambiguity disappears and the weak interaction result describes well the experiment. It is, hence, the transition region r c ^b, where the transition from strong to weak interaction takes place. 
  Reference    Z. Naturforsch. 47a, 629—636 (1992); received December 31 1991 
  Published    1992 
  Keywords    Landau collision operator, Collision frequency, Magnetized plasma, Weak coupling theory, Strong coupling theory 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0629.pdf 
 Identifier    ZNA-1992-47a-0629 
 Volume    47 
108Author    O. Lutz, M. PfefferRequires cookie*
 Title    Large Volume NMR Spectroscopy with a Whole Body Imager  
 Abstract    A whole body NMR imager (1.5 T) has been operated with large samples and a home built coil to study NMR signals of heteronuclei at very low concentrations. Typical examples of 27 A1, 51 V, and 8 'Br are given, signals of 1 pmolal aqueous solutions of e.g. NaVÖ 3 can be detected. 129 Xe was observed in xenon gas at atmospheric pressure with one scan. A 129 Xe gaseous state NMR image is presented in a xenon containing sample. Also some typical measurements of longitudinal relax-ation times of 27 Al, 51 V, and 129 Xe are given. 
  Reference    Z. Naturforsch. 47a, 637 (1992); received February 29 1992 
  Published    1992 
  Keywords    Heteronuclear MR, Gaseous state NMR imaging, Large volume, Low concentration, 129 Xe gas 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0637.pdf 
 Identifier    ZNA-1992-47a-0637 
 Volume    47 
109Author    P. Fischer, H. Port, H. C. WolfRequires cookie*
 Title    Fluoreszenz-Spektroskopie an dünnen im UHV aufgedampften Coronen-Schichten  
 Abstract    Fluorescence Spectroscopy on UHV-Deposited Thin Films of Coronene Thin films of coronene, UHV-deposited on different inorganic substrates (Si(l 11), Si(100), Si/Si0 2 , graphite(OOOl) and MoS 2 (0001)) have been investigated via laser induced fluorescence and fluores-cence excitation spectra at various coronene coverages (from submonolayers to 1000 Ä) and temper-atures (4.2 K-300 K). Independent of the substrate the films reveal a characteristic absorption which is red-shifted with respect to that of the coronene crystal and is attributed to a new film-specific structural modification (in accord with X-ray data). At film thicknesses d > 50 Ä this absorption is increasingly superimposed by crystal-type absorption. The fluorescence spectra at low coverages and low temperatures strongly depend on the substrate. On Si/Si0 2 , graphite and MoS 2 the fluorescence is similar to that of the coronene crystal. Thin films on Si(100) and Si(lll), on the other hand, show monomer-like narrowband fluorescence originating, presumably, in substrate-induced trap states. 
  Reference    Z. Naturforsch. 47a, 643—659 (1992); received April 2 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0643.pdf 
 Identifier    ZNA-1992-47a-0643 
 Volume    47 
110Author    F. Temps, H. Gg, M. Wagner, WolfRequires cookie*
 Title    Far-Infrared Laser Magnetic Resonance Detection of CH 2 C1  
 Abstract    New Far Infrared Laser Magnetic Resonance (LMR) spectra have been detected in the reaction of Cl atoms with CH 2 CO. Based on chemical and kinetic evidence they were assigned to CH 2 C1 radicals. The assignment was substantiated by subsequent experiments which employed the reac-tions of F atoms with CH 3 C1 and Na atoms with CH 2 C1 2 , respectively. The three different sources yielded identical spectra. 
  Reference    Z. Naturforsch. 47a, 660—664 (1992); received February 6 1992 
  Published    1992 
  Keywords    Laser Magnetic resonance, Radicals, Rotational spectroscopy 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0660.pdf 
 Identifier    ZNA-1992-47a-0660 
 Volume    47 
111Author    J. P. AmoureuxRequires cookie*
 Title    NMR Characterization of Half-integer Quadrupolar Nuclei in Solids  
 Abstract    This article describes a few aspects of NMR characterization of half-integer quadrupolar nuclei in powder samples which are either static or rotating around one fixed axis (M.A.S. and V.A.S. techniques). The simultaneous occurence of C.S.A. and quadrupole interactions with possible non-coincident tensors is discussed. Two experimental limitations are taken into accout: the sample spinning speed and the RF-am-plifier power. Physics Abstract code numbers: 0758, 
  Reference    Z. Naturforsch. 47a, 665—674 (1992); revised version received February 5 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0665.pdf 
 Identifier    ZNA-1992-47a-0665 
 Volume    47 
112Author    Kazuo Igarashi, Koji Tajiri, Tadashi Asahina, Mineo Kosaka, Yasuhiko Iwadate, Junichi MochinagaRequires cookie*
 Title    Surface Tension Around Eutectic Compositions of Molten Alkali Carbonate Mixtures  
 Abstract    The surface tension around the eutectic composition of molten binary and ternary mixtures composed of Li 2 C0 3 with Na 2 C0 3 and/or K 2 C0 3 has been measured by the maximum bubble pressure method. The surface tensions of all the three systems were represented as functions of temperature. 
  Reference    Z. Naturforsch. 47a, 675—677 (1992); received February 25 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0675.pdf 
 Identifier    ZNA-1992-47a-0675 
 Volume    47 
113Author    U. Witt, M. Stockhausen, J. Jadżyn, P. KędzioraRequires cookie*
 Title    Dielectric Relaxation of 2-Amino-l-butanol  
 Abstract    The dielectric relaxation spectrum of the title substance in mixtures with 1,4-dioxane or benzene (pure liquid to moderate mixture ratios) is measured between 5 MHz and 36 GHz at 20°C. The static permittivity is determined over the whole mixture range. The results are discussed in particular with respect to the possibility that different types of hydrogen bonded aggregations may contribute to the main relaxation. 
  Reference    Z. Naturforsch. 47a, 678—680 (1992); received March 17 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0678.pdf 
 Identifier    ZNA-1992-47a-0678 
 Volume    47 
114Author    W. Stahl, J.-U GrabowRequires cookie*
 Title    The Rotational Spectrum of the Fluorobenzene-Argon Van der Waals Complex  
 Abstract    The rotational spectrum of the fluorobenzene-argon complex has been studied in the microwave region between 7 and 18 GHz using a pulsed molecular beam microwave Fourier transform spec-trometer. The rotational constants were found to be A = 1811.81369(11) MHz, B= 1105.12965(15) MHz, C = 901.84281(5) MHz, the centrifugal distortion constants are A } = 2.6886(17) kHz, A JK = 8.3761 (52) kHz A K = —8.278(5) kHz, <5, =0.65993(72) kHz, and ^ = 6.013(11) kHz. The argon atom is placed 3.55 A above the ring plane. 
  Reference    Z. Naturforsch. 47a, 681—684 (1992); received February 24 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0681.pdf 
 Identifier    ZNA-1992-47a-0681 
 Volume    47 
115Author    M. Bionducci, F. Buffa, G. Licheri, G. NavarraRequires cookie*
 Title    Testing the Reverse Monte Carlo Method Using Scattering Data from Amorphous Ni 2 Zr  
 Abstract    The reverse Monte Carlo simulation has been tested by modelling the partial distribution functions of amorphous Ni 2 Zr. Three runs of simulation involving experimental data from isotopic substitutions neutron scattering and X-ray anomalous scattering are presented. 
  Reference    Z. Naturforsch. 47a, 685—688 (1992); received February 3 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0685.pdf 
 Identifier    ZNA-1992-47a-0685 
 Volume    47 
116Author    Günter Burbach, Norbert Weiden, Alarich WeissRequires cookie*
 Title    Molecular Motions in Solid [Sb(CH 3 ) 4 ]PF 6 . A Combined 19 F Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Study  
 Abstract    The molecular dynamics of tetramethylstibonium hexafluorophosphate, [Sb(CH 3) 4 ]PF 6 , is inves-tigated over a broad temperature range. NMR spin lattice relaxation times and the NMR second moments of the *H and F nuclei were determined in the range 8.6 < T/K ^ 332.3 for polycrystalline [Sb(CH 3) 4 ]PF 6 . The complex cation undergoes isotropic tumbling for T>260 K and thermally activated methyl group rotation in the temperature range T< 196 K. The activation energies for the transition from methyl group rotation to cation reorientation, as derived from NMR wideline (18.1 kJ/mol) and relaxation (22.7 kJ/mol) measurements, match. At very low temperatures pseudo classical line narrowing is observed, indicating tunneling motions of the methyl groups. The exis-tence of two crystallographically inequivalent methyl groups is found by X-ray structure analysis at room temperature. The space group is P6 3 mc, Z = 2; a = 738.6 pm, c = 1089.3 pm. It is confirmed by two steps in the temperature dependence of the signal intensity of the quasielastic line in neutron fixed window measurements in the temperature range 2 < T/K <148. The low temperature spin lattice relaxation times can be explained qualitatively by contributions of two crystallographically inequivalent methyl groups. Apparent activation energies for the two crystallographically different methyl groups are estimated. The complex anion undergoes isotropic tumbling in the temperature range 95 < T/K < 330. Above 330 K additionally translational motion is activated. Below 95 K the rotational motion of PF 6 e is freezing in via an uniaxial state in range 40 < T/K <80. Activation energies for both isotropical tumbling (10.5 kJ/mol) and uniaxial rotation (5.8 kJ/mol) have been derived from 19 F NMR spin lattice relaxation. 
  Reference    Z. Naturforsch. 47a, 689—701 (1992); received January 16 1992 
  Published    1992 
  Keywords    Complex compounds, Molecular dynamics, Rotational tunneling, Nuclear magnetic resonance spectroscopy, Quasielastic neutron scattering 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0689.pdf 
 Identifier    ZNA-1992-47a-0689 
 Volume    47 
117Author    Shulamith Schlick, BrianE. Myers, Lars Sjöqvist, Anders LundRequires cookie*
 Title    Solvation Structure of the Ti(III) Ion in Methanol Solutions and in Perfluorinated Ionomers Swollen by Water and Methanol. A Study by ESR and ENDOR  
 Abstract    The local environment of Ti 3+ cations in methanol solutions and in Nafion perfluorinated ionomers swollen by water and methanol has been studied by electron spin resonance (ESR) and by *H and 2 H electron nuclear double resonance (ENDOR) spectroscopies. The two major sites reflecting the ligation of the cations as a function of solvent structure and cation concentration have been analyzed, using whenever possible the method of orientation selection for the ENDOR transi-tions. The distance R N of the protons from the central cation, and the angle 0 N between the symmetry axis of Ti 3+ and the Ti 3 + -proton vector have been deduced by evaluating the dipolar interaction tensor and by simulating the orientation dependence of the ENDOR signal. For site 1 of Ti 3+ in methanol {g n = 1.986 and g L = 1.894) no orientation selection was possible, and R N values in the range 4.1 to 4.6 Ä are suggested from the ENDOR splittings. For site 2 of Ti 3+ in methanol (011 = 1.943 and g L = 1.960) equatorial and axial methyl protons have been detected; the R N values deduced from the simulations are 3.95 and 4.35 Ä, respectively. For Ti 3+ in Nafion swollen by water (g || = 1.997 and g L = 1.907), equatorial and axial protons from OH groups have been detected, and the ENDOR spectra were simulated with R N values of 2.60 and 3.10 A respectively for these protons. 
  Reference    Z. Naturforsch. 47a, 702—712 (1992); received January 24 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0702.pdf 
 Identifier    ZNA-1992-47a-0702 
 Volume    47 
118Author    Noriaki Okubo, Harutaka Sekiya, Chiaki Ishikawa, Yoshihito AbeRequires cookie*
 Title    Br Nuclear Quadrupole Relaxation in the High Temperature Modification of Niobium Pentabromide  
 Abstract    The spin-lattice relaxation time of 79 Br NQR has been measured between 4.2 K and room temperature. The result is compared with that of 35 C1 NQR in NbCl 5 . The origin of the relaxation is attributed to the quadrupolar interaction and the temperature dependence is explained by the Raman process. The Debye temperature is determined to be 94 K and the relaxation time is related with the NQR frequency through the covalency. 
  Reference    Z. Naturforsch. 47a, 713—720 (1992); received December 13 1991 
  Published    1992 
  Keywords    Niobium pentabromide, Nuclear quadrupole resonance, Spin-lattice relaxation, Raman process, Debye temperature 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0713.pdf 
 Identifier    ZNA-1992-47a-0713 
 Volume    47 
119Author    S. Torre, P. FerloniRequires cookie*
 Title    Molecular Motion in Solid Tetramethylammonium Tetrafluoroborate  
 Abstract    Measurements of n B and NMR relaxation times, differential scanning calorimetry and thermomechanical analysis, carried out on polycrystalline (CH 3) 4 NBF 4 from room temperature to about 100 K, have permitted to discuss the crystal dynamics of this salt and to analyze the nature of the phase transition occurring at «150K. Moreover, by means of an evaluation of the n B quadrupole coupling constant, information about the position of the F atoms has been obtained. An explanation of the NMR data in terms of an order-disorder phase transition involving the F~ ions is given. 
  Reference    Z. Naturforsch. 47a, 721—727 (1992); received March 24 1992 
  Published    1992 
  Keywords    (CH 3 ) 4 NBF 4, Molecular motion, Phase transition 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0721.pdf 
 Identifier    ZNA-1992-47a-0721 
 Volume    47 
120Author    Wolfgang Windsch, Horst Braeter, JulioA. GonzaloRequires cookie*
 Title    Application of the Pseudo-Spin Model to the Lowest-Temperature Phase Transition of the Mixed Crystal (NH 4 ) 2(1 _ x) K 2x Pb[Cu(N0 2 ) 6 ]  
 Abstract    Mizuno et al. developed a jumping model to explain the nonlinear decrease of the phase transition temperature in the mixed crystals (NH 4) 2(1 _ ;c) K 2x Pb[Cu(N0 2) 6 ] with 0 fS x ^ 1. Their implications and results are compared with model parameters and with the results of calculation within the Ising model with transverse field. It comes out that the assumption of a temperature independent transient time in the jumping model corresponds to the admission of tunneling in the Ising model. 
  Reference    Z. Naturforsch. 47a, 728—732 (1992); received April 7 1992 
  Published    1992 
  Similar Items    Find
 DEBUG INFO      
 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0728.pdf 
 Identifier    ZNA-1992-47a-0728 
 Volume    47 
Prev
...
6
7
8
9
10
...
Next