| | 82 | Author
| Motohiro Mizuno, Tetsuo Asaji, Daiyu Nakamura, Keizo Horiuchi | Requires cookie* | | | Title
| C1 NQR Spin-Lattice Relaxation in Paramagnetic CuPtCl 6 '6H 2 0  | | | | Abstract
| 35 C1 NQR spin-lattice relaxation times T lQ of paramagnetic CuPtCl 6 • 6H 2 0 were measured as a function of temperature. Below the cooperative Jahn-Teller phase transition at T c = 136 K, an almost temperature independent T 1Q between 0.6 and 1 ms was obtained for each line of the triplet observed. This suggests that the nuclear spin-lattice relaxation of chlorine is dominantly determined by magnetic dipolar interactions between chlorine nuclei and electron spins. No marked anomaly in the nuclear relaxation rate was detected at T c . Above T c , T 1Q for the single 35 C1 NQR line increased from 0.6 ms at T c to 1-4 ms at 365 K. The rapid T lQ decrease observed above ca. 390 K can be attributed to a reorientational motion of the [PtCl 6 ] 2 ~ anion with an activation energy of 1.1 xlO 2 kJmol" 1 . | | | |
Reference
| Z. Naturforsch. 45a, 527—530 (1990); received August 25 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0527.pdf | | | | Identifier
| ZNA-1990-45a-0527 | | | | Volume
| 45 | |
| 84 | Author
| Mariusz Máckowiak, Costas Dimitropoulos | Requires cookie* | | | Title
| Calculation of NQR v's and T l s being proportional to T 4 and T 5 , respectively | | | | Abstract
| The second-order Raman phonon process for a multilevel spin system is shown to give a quadru-polar spin-lattice relaxation rate T x ~ varying as T 5 at very low temperatures. This relaxation rate for quadrupole spins is similar to the one discussed for a paramagnetic spin system having a multilevel ground state. The temperature dependence of Tj is discussed on the basis of some simplifying assumptions about the nature of the lattice vibrations in the Debye approximation. This type of relaxation process has been observed below 20 K in tetramethylammonium hydrogen bis-trichloroacetate for the 35 C1 Ti _1 . Below 20 K the NQR frequency in the same crystal reveals a T 4 temperature dependence due to the induced modulations of the vibrational and librational coordinates by the low-frequency acoustic phonons. | | | |
Reference
| Z. Naturforsch. 45a, 536—540 (1990); received August 22 1989 in revised form November 24 1989 | | | |
Published
| 1990 | | | |
Keywords
| Quadrupole relaxation, low temperature, NQR | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0536.pdf | | | | Identifier
| ZNA-1990-45a-0536 | | | | Volume
| 45 | |
| 85 | Author
| Hideaki Chihara, Nobuo Nakamura | Requires cookie* | | | Title
| Antimony NQR and Nuclear Magnetic Relaxation in Hexaammonium Dodecafluorotrisulfatotetraantimonate (III), (NH 4 ) 6 Sb 4 (S0 4 ) 3 F 12 | | | | Abstract
| Antimony nuclear quadrupole resonance frequencies in (NH 4) 6 Sb 4 (S0 4) 3 F 12 crystals were mea-sured as a function of temperature, and no evidence of phase transition was detected between 77 K and room temperature. However, the resonance frequencies do not follow the Bayer type exactly. Such an anomaly is attributed to the effect of rotation of ammonium ions which form hydrogen bonds of types N —H • • • F and N —H • • -O. In fact, the spin-lattice relaxation time of X H and 19 F has a minimum which is ascribed to the reorientation of NH 4 with an activation energy of 7.14 kJ mol -1 . The switch model for the electric field gradient at Sb nuclei was examined. | | | |
Reference
| Z. Naturforsch. 45a, 541—544 (1990); received September 3 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0541.pdf | | | | Identifier
| ZNA-1990-45a-0541 | | | | Volume
| 45 | |
| 86 | Author
| VirendraK. Sharma, Werner Richarz, Surendra Sharma, Alarich Weiss | Requires cookie* | | | Title
| A NQR Study of y-alumina Containing Chemisorbed Cl 2 | | | | Abstract
| Cl 2 was adsorbed at 370 and 870 K on commercially available y-alumina, with BET surface area of 180m 2 /g, after dehydration at 850 K. NQR measurements were carried out between 55 and 6 MHz. The sample containing Cl ? chemisorbed at 870 K showed the presence of a set of quite strong NQR signals with frequencies lower than 10.6 MHz, and another set of very weak NQR signals between 18.5 and 13.0 MHz. The stronger signals have been inferred as due to Al and have been assigned to Al in three distinct environments. The values of e 2 Qq/h and ^ determined for the signals are (1) 35.9 MHz, 0.53; (2) 35.7 MHz, 0.74; and (3) 35.3 MHz, 0.0 respectively. These values of e 2 Qq/h are found to be very high as compared to those estimated for 27 A1 at distorted octahedral and tetrahedral sites of the alumina, viz. 3.5 and 4.0 MHz respectively, from MAS-NMR. Therefore, chemisorption causes 27 A1 to exist in the surface region at sites with greater distortion than in the interior of the particles but much smaller than in the case of completely dehydrated samples for which no NQR signals could be observed. The weak signals have been tentatively attributed to 35 C1. The present results demonstrate that the NQR technique can be used in studies of chemically bound species on heterogenous catalysts. | | | |
Reference
| Z. Naturforsch. 45a, 545—549 (1990); received August 22 1989 | | | |
Published
| 1990 | | | |
Keywords
| Nuclear Quadrupole Resonance, Chemisorption, 35 C1, 27 A1, y-Alumina | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0545.pdf | | | | Identifier
| ZNA-1990-45a-0545 | | | | Volume
| 45 | |
| 87 | Author
| Theresa Varty, R. Julian, C. Brown, FrancisP. Temme | Requires cookie* | | | Title
| Optimal Zeeman-NQR Powder Lineshape Calculations for 3/2^/^7/2 | | | | Abstract
| The powder lineshapes, associated with Zeeman-NQR A\m\= +1 transitions for half-integer spin from 3/2 and 7/2 are derived using an optimized (6, (j)) sampling algorithm for the intensity response. The 1 = 3/2 system is examined over the full asymmetry range, whereas the I >3/2 lineshapes are calculated for rj^0.35. The algorithm adopted is modelled on the concepts in the earlier NMR lineshape calculations of Alderman, Solum, and Grant**. | | | |
Reference
| Z. Naturforsch. 45a, 550—558 (1990); received August 23 1989 | | | |
Published
| 1990 | | | |
Keywords
| NQR, Zeeman, quadrupole, powder, lineshape | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0550.pdf | | | | Identifier
| ZNA-1990-45a-0550 | | | | Volume
| 45 | |
| 88 | Author
| V. S. Grechishkin | Requires cookie* | | | Title
| New Methods of Nuclear Quadrupole Resonance | | | | Abstract
| New NQR methods, developed over the past years, are discussed: 1. Two frequency NQR double resonance, 2. the influence of strong off-resonance combination of rf pulses on demagnetized state in NQR, 3. remote NQR. | | | |
Reference
| Z. Naturforsch. 45a, 559—564 (1990); received August 23 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0559.pdf | | | | Identifier
| ZNA-1990-45a-0559 | | | | Volume
| 45 | |
| 91 | Author
| R. Böttcher, D. Heinhold, W. Windsch | Requires cookie* | | | Title
| Strong Quadrupole Interaction in ENDOR Spectroscopy | | | | Abstract
| If the nuclear quadrupole interaction H Q of the ligands exceeds the magnetic hyperfine H hf and nuclear Zeeman H NZ interaction (H Q > H hf + H nz), ENDOR spectra show the same behaviour as Zeeman field perturbed NQR spectra. The angular dependence of the transition frequencies and the transition probabilities of such ENDOR spectra for axial symmetry are calculated and applied to analyze the 35 -37 Cl distant ENDOR spectra of gamma-irradiated NaC10 3 single crystals. | | | |
Reference
| Z. Naturforsch. 45a, 570—574 (1990); received August 22 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0570.pdf | | | | Identifier
| ZNA-1990-45a-0570 | | | | Volume
| 45 | |
| 92 | Author
| GerardS. Harbison, Andris Slokenbergs | Requires cookie* | | | Title
| Two-dimensional Nutation Echo Nuclear Quadrupole Resonance Spectroscopy | | | | Abstract
| We discuss two new two-dimensional nuclear quadrupole resonance experiments, both based on the principle of nutation spectroscopy, which can be used to determine the asymmetry parameter, and thus the full quadrupolar tensor, of spin-3/2 nuclei at zero applied magnetic field. The first experiment is a simple nutation pulse sequence in which the first time period (r t) is the duration of the radiofrequency exciting pulse; and the second (t 2) is the normal free-precession of a quadrupolar nucleus at zero-field. After double Fourier-transformation, the result is a 2 D spectrum in which the first frequency dimension is the nutation spectrum for the quadrupolar nucleus at zero-field. For polycrystalline samples this sequence generates powder lineshapes; the position of the singularities, in these lineshapes can be used to determine the asymmetry parameters t] in a very straightforward manner, q has previously only been obtainable using Zeeman perturbed NQR methods. The second sequence is the same nutation experiment with a spin-echo pulse added. The virtue of this refocussing pulse is that it allows acquisition of nutation spectra from samples with arbitrary inhomogeneous linewidth; thus, asymmetry parameters can be determined even where the quadrupolar resonance is wider than the bandwidth of the spectrometer. Experimental examples of 35 C1, 8 'Br and 63 Cu nutation and nutation-echo spectra are presented. | | | |
Reference
| Z. Naturforsch. 45a, 575—580 (1990); received August 25 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0575.pdf | | | | Identifier
| ZNA-1990-45a-0575 | | | | Volume
| 45 | |
| 93 | Author
| A. Ramamoorthy, P. T. Narasimhan | Requires cookie* | | | Title
| Numerical Design of Composite Pulses for Polycrystalline Samples in Pulsed NQR Spectroscopy | | | | Abstract
| The density matrix approach along with fictitious spin-1/2 or tensor operator formalisms were employed to obtain general expressions for </ x > and thus the signal induced in a coil in the case of physically equivalent non-interacting spin I = 1 and 3/2 nuclei in a single crystal with a three-pulse composite pulse. The corresponding powder averages were then obtained and the dependence of the signal on the i-th pulse flip angle (0,) and phase (0,) studied. A numerical procedure established the optimum "TT/2" composite pulse for polycrystalline samples as (90) o -(70) 45 -(20) 25 , where the quan-tity in parentheses denotes the flip angle and the subscript the phase. A two-pulse composite pulse of the form (126) 0 -(300) 80 was also inferred, but the three-pulse composite pulse is superior. These composite pulses are shown to have general validity for other spin I values. | | | |
Reference
| Z. Naturforsch. 45a, 581—586 (1990); received August 24 1989 in revised form December 6 1989 | | | |
Published
| 1990 | | | |
Keywords
| Composite pulses, NQR spectroscopy, Polycrystalline samples, Numerically designed pulses | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0581.pdf | | | | Identifier
| ZNA-1990-45a-0581 | | | | Volume
| 45 | |
| 94 | Author
| Y. L. Zhuang, R. A. Marino | Requires cookie* | | | Title
| Line Narrowing in Nitrogen-14 NQR by Non-Resonant Irradiation* * | | | | Abstract
| The effect of non-resonant irradiation on the linewidth of 14 N NQR lines has been investigated in three cases with zero asymmetry parameter. The characteristic time of the free induction decay (T 2 *) in Trimethylamine (TMA), Triethylenediamine (TED) and Hexamethylenetetramine (HMT) was studied at 77 K. Circularly polarized non-resonant irradiations of 11 kHz were used with intensities of up to 24 G with a geometrical arrangement following Ito and Hashi. The largest effect, a 100% increase in T*, is measured in TMA. No observable effect occurs in HMT. An intermediate result occurs in TED, where the considerable narrowing caused by the non-resonant field serves to provide a greater resolution of the fine structure first reported by Colligiani and Ambrosetti. This fine structure, presumably dipolar in origin, is not itself affected by the non-resonant irradiation. The degree to which the theory of dressing fields can account for these results is discussed. | | | |
Reference
| Z. Naturforsch. 45a, 587—590 (1990); received August 25 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0587.pdf | | | | Identifier
| ZNA-1990-45a-0587 | | | | Volume
| 45 | |
| 95 | Author
| Yushi Zikumaru | Requires cookie* | | | Title
| NQR Spectrometer with a Two Integrated Circuits Radio Frequency Head | | | | Abstract
| An NQR spectrometer has been constructed using two linear integrated circuits in its oscillator-detector. This is very simple and compact and works in range 3-65 MHz. The radio frequency voltage can be varied from 10mV p _ p to 15 V p _ p by changing the supply-voltage of an integrated circuit pA 733. The utility of the spectrometer is demonstrated by recording 35 C1 NQR spectra in p-C 6 H 4 Cl 2 , NaC10 3 , and KC10 3 . | | | |
Reference
| Z. Naturforsch. 45a, 591—594 (1990); received August 23 1989 in revised form November 16 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0591.pdf | | | | Identifier
| ZNA-1990-45a-0591 | | | | Volume
| 45 | |
| 96 | Author
| M.M P Khurshid, F. Zhenye, J.A S Smith | Requires cookie* | | | Title
| A Low-Temperature High-Sensitivity Field-Cycling Spectrometer for Quadrupole Double Resonance Spectroscopy | | | | Abstract
| This paper discusses the design of a variable-temperature high-sensitivity field cycling spectrom-eter for nuclear magnetic resonance and nuclear quadrupole double resonance experiments. The instrument is capable of detecting N-14 quadrupole resonance signals from samples as small as 0.1 g down to temperatures of 150 K. The magnetic field cycling is performed by mechanical transfer of the sample using a pair of switchable electromagnetic solenoids, in times of about 0.2 s. | | | |
Reference
| Z. Naturforsch. 45a, 595—598 (1990); received January 26 1990 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0595.pdf | | | | Identifier
| ZNA-1990-45a-0595 | | | | Volume
| 45 | |
| 97 | Author
| Osamu Ege, Hisao Negita | Requires cookie* | | | Title
| Zeeman NQR Studies on Powdered Bromine Compounds Having Small tj | | | | Abstract
| The Zeeman NQR of 79 Br and 81 Br in samples having relatively small r\ was studied on several bromine compounds which were in the powder or polycrystal state. The absorption lines were detected in the integral form by the bridge circuit. When a static magnetic field was applied, the line shapes were broadened and usually two dips appeared symmetrically at both sides of the zero field line. The values of rj were estimated from the patterns of the dips. For compounds such as NaBr0 3 , however, as expected no dips were observed. | | | |
Reference
| Z. Naturforsch. 45a, 599—602 (1990); received August 26 1989 in revised form November 24 1989 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0599.pdf | | | | Identifier
| ZNA-1990-45a-0599 | | | | Volume
| 45 | |
| 98 | Author
| S. J. Camargo, H. Tasso | Requires cookie* | | | Title
| Self-Similar Statistics in MHD Turbulence | | | | Abstract
| The fully developed decaying turbulence of 3-d resistive, viscous, incompressible magnetohydro-dynamics is investigated using Elsasser variables and Hopf equation for probability distributions. The method is an extension of a previous work for Navier Stokes equations done by Foias et al. based on a suggestion by Hopf. It uses essentially self-similar properties of the statistics, which "almost" determine the turbulence spectrum up to a mild assumption on an unknown function. This spectrum is the well known Kolmogorov spectrum. | | | |
Reference
| Z. Naturforsch. 45a, 603—608 (1990); received February 15 1990 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0603.pdf | | | | Identifier
| ZNA-1990-45a-0603 | | | | Volume
| 45 | |
| 99 | Author
| D. Correa-Restrepo | Requires cookie* | | | Title
| Compressibility and Resistive Ballooning Modes | | | | Abstract
| For equilibria stable with respect to ideal ballooning modes it is shown by means of a simple argument that, owing to plasma compressibility, resistive ballooning modes with small growth rates can only exist if they are extended along a field line. In particular, a small region of bad curvature along a field line is not sufficient for the existence of unstable modes. | | | |
Reference
| Z. Naturforsch. 45a, 609—610 (1990); received January 16 1990 | | | |
Published
| 1990 | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0609.pdf | | | | Identifier
| ZNA-1990-45a-0609 | | | | Volume
| 45 | |
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