| | 101 | Author
| Jan Szczepanski, Robert Pellow, Martin Vala | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0595.pdf | | | | Identifier
| ZNA-1992-47a-0595 | | | | Volume
| 47 | |
| 102 | Author
| Szilvia Murányi, Zoltän Noszticzius | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0605.pdf | | | | Identifier
| ZNA-1992-47a-0605 | | | | Volume
| 47 | |
| 103 | Author
| Martin Ystenes, Wolfgang Brockner, Frank Menzel | Requires 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£ - | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0614.pdf | | | | Identifier
| ZNA-1992-47a-0614 | | | | Volume
| 47 | |
| 104 | Author
| Hans Sallhofer | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0619.pdf | | | | Identifier
| ZNA-1992-47a-0619 | | | | Volume
| 47 | |
| 106 | Author
| M. A. Osipov, E. M. Terentjev | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0627_n.pdf | | | | Identifier
| ZNA-1992-47a-0627_n | | | | Volume
| 47 | |
| 107 | Author
| H. Schamel, G. Hübner | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0629.pdf | | | | Identifier
| ZNA-1992-47a-0629 | | | | Volume
| 47 | |
| 108 | Author
| O. Lutz, M. Pfeffer | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0637.pdf | | | | Identifier
| ZNA-1992-47a-0637 | | | | Volume
| 47 | |
| 109 | Author
| P. Fischer, H. Port, H. C. Wolf | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0643.pdf | | | | Identifier
| ZNA-1992-47a-0643 | | | | Volume
| 47 | |
| 111 | Author
| J. P. Amoureux | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0665.pdf | | | | Identifier
| ZNA-1992-47a-0665 | | | | Volume
| 47 | |
| 112 | Author
| Kazuo Igarashi, Koji Tajiri, Tadashi Asahina, Mineo Kosaka, Yasuhiko Iwadate, Junichi Mochinaga | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0675.pdf | | | | Identifier
| ZNA-1992-47a-0675 | | | | Volume
| 47 | |
| 113 | Author
| U. Witt, M. Stockhausen, J. Jadżyn, P. Kędziora | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0678.pdf | | | | Identifier
| ZNA-1992-47a-0678 | | | | Volume
| 47 | |
| 114 | Author
| W. Stahl, J.-U Grabow | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0681.pdf | | | | Identifier
| ZNA-1992-47a-0681 | | | | Volume
| 47 | |
| 116 | Author
| Günter Burbach, Norbert Weiden, Alarich Weiss | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0689.pdf | | | | Identifier
| ZNA-1992-47a-0689 | | | | Volume
| 47 | |
| 117 | Author
| Shulamith Schlick, BrianE. Myers, Lars Sjöqvist, Anders Lund | Requires 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 | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0702.pdf | | | | Identifier
| ZNA-1992-47a-0702 | | | | Volume
| 47 | |
| 119 | Author
| S. Torre, P. Ferloni | Requires 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 | | | |
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| | | | | TEI-XML for
| default:Reihe_A/47/ZNA-1992-47a-0721.pdf | | | | Identifier
| ZNA-1992-47a-0721 | | | | Volume
| 47 | |
|
