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1Author    G. Wulfsberg, K. Shadid, B. Farris, J. Monn, T. Bonner, J. Yanisch, Al WeissRequires cookie*
 Title    Dioxin Precursors: NQR Studies of Group 1 and Related 2,6-Dichlorophenolate and 2,4,6-Trichlorophenolate Salts  
 Abstract    The 81 Br and 35 C1 NQR spectra of anhydrous Group 1, tetraalkylammonium, and thallium(I) 2,6-dichlorophenolates, 2,4,6-trichlorophenolates, and 4-bromo-2,6-dichlorophenolates were searched for evidence of solid-state cation-organochlorine interactions that might, for example, be (in part) responsible for the difference in the thermal decomposition reactions of these salts (to give the supertoxic environmental pollutants, the polychlorinated dibenzodioxins) versus those of the corresponding Group 11 chlorophenolate complexes, which do not decompose to dioxins. For cations ranging in size from tetraethylammonium to potassium, the total range of 35 C1 NQR frequencies in 2,6-dichlorophenolate and 2,4,6-trichlorophenolate salts is only 1.401 MHz, which, although larger than the 0.7 MHz range likely in molecular chlorocarbons, is smaller than in individual chlorophenolates of copper(I) and silver(I) (up to 2.0 MHz). In sodium and thallium(I) 2,4,6-trichlorophenolates substantially large frequency shifts (ca. 2.0 MHz) occur, to higher frequen-cies for the para-chlorines and lower frequencies for the ortho-chlorines (Na only). These disappear even in closely related compounds and show a pattern that seems unrelated to the decomposition products of the chlorophenolates. 
  Reference    Z. Naturforsch. 47a, 153—159 (1992); received July 16 1991 
  Published    1992 
  Keywords    Chlorophenolates, Nuclear quadrupole resonance, Dioxin 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0153.pdf 
 Identifier    ZNA-1992-47a-0153 
 Volume    47 
2Author    M. Ariusz, M. Aćkow Iak, M. Arek BojarskiRequires cookie*
 Title    Automatically Tuned Probe Head System for Pulsed NQR Spectroscopy in Extreme Thermodynamic Conditions * M ich ał O stafin  
 Abstract    A com plete N Q R probe-head system operating in the frequency ranges 0 .5 -1 5 0 and 150— 300 M H z is described. The head is particularly suited for N Q R experiments carried out at a remote location, for example in a low-temperature cryostat or high-pressure chamber. M oreover, the head system includes a microprocessor-controller for automated tuning of the probe to the operating frequency of the associated N Q R spectrometer. The controller can be easily interfaced to a PC via standard serial port. 
  Reference    Z. Naturforsch. 49a, 42 (1994); received July 23 1993 
  Published    1994 
  Keywords    Nuclear quadrupole resonance, Pulsed spectrometers, Instrum entation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0042.pdf 
 Identifier    ZNA-1994-49a-0042 
 Volume    49 
3Author    G. L. Petersen, P. J. Bray, R.A M ArinoRequires cookie*
 Title    A New Pulsed Nuclear Quadrupole Resonance Spectrometer  
 Abstract    A new pulsed nuclear quadrupole resonance spectrometer is described and a number of Nitrogen-14 spectra are shown and discussed. The spectrometer is computer interfaced and both data acqui­ sition and all adjustments other than the matching network tuning are automatic. Spectra may be produced using fast Fourier transforms or by the Clark Method. The latter is particularly valuable when very wide line widths are encountered. 
  Reference    Z. Naturforsch. 49a, 65—7 (1994); received November 18 1993 
  Published    1994 
  Keywords    Nuclear quadrupole resonance, Spectrometer, Instrumentation, Fourier transform 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0065.pdf 
 Identifier    ZNA-1994-49a-0065 
 Volume    49 
4Author    Nicolai Sinyavsky, Michal Ostafin, Mariusz MaćkowiakRequires cookie*
 Title    Rapid Measurement of Nutation NQR Spectra in Powders Using an RF Pulse Train  
 Abstract    The method of two-dimensional nutation NQR spectroscopy, introduced by Harbison in 1989, has been successfully used for determining of the asymmetry parameter of the EFG tensor for spin-3/2 nuclei in both powdered and monocrystal samples in the absence of an external magnetic field. The inconvenience inherent in the method, however, is the long time required, because data acquisition must be repeated for various RF pulse lengths. We discuss a method to reduce the time of the nutation experiment by using a sequence of identical short RF pulses of length r w and distance t. It is shown that for an NQR frequency co 0 , frequency offset Aco, and pulse parameters satisfying the relation co 0 1 -I-Aco t w = 2 n k (k = 1, 2, 3,..., n) a synchronism of pulse action takes place and the nutation interferogram can be measured "stroboscopically" between the pulses. The maximum time saving factor that can be obtained as compared to the conventional nutation experiment is of the order of the number of pulses used in a pulse train. The method has been successfully applied for determination of the asymmetry parameter for one of the two 35 C1 sites in polycrystalline 2,4,6-trichloro-l,3,5-triazine (cyanuric chloride). 
  Reference    Z. Naturforsch. 51a, 363—367 (1996); received February 13 1996 
  Published    1996 
  Keywords    Nuclear quadrupole resonance, Two-dimensional nutation spectroscopy, Asymmetry parameter 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0363.pdf 
 Identifier    ZNA-1996-51a-0363 
 Volume    51 
5Author    N. Sinyavsky, M. Maćkowiak, N. VelikiteRequires cookie*
 Title    Influence of the rf Field Inhomogeneity on Nutation NQR Spectra of Spin 3/2 Nuclei in Powders  
 Abstract    The influence of the rf field inhomogeneity on the NQR nutation spectra of spin / = 3/2 nuclei in powder samples is investigated. To eliminate the rf field inhomogeneity effects, a method of reconstruction of the NQR nutation spectra, based on finding the deconvolution of the Fourier nutation spectrum with a function of the rf field distribution, is used. The method is successfully demonstrated for simulated and experimental NQR nutation spectra of 35 C1 in TiCl 4 . The lineshape analysis of reconstructed nutation spectra allowing the determination of the EFG asymmetry parameter is given. The real advantage of the proposed method is that the high-resolution nutation spectrum may be obtained for a sample filling up the entire coil. 
  Reference    Z. Naturforsch. 54a, 153—158 (1999); received November 24 1998 
  Published    1999 
  Keywords    Nuclear Quadrupole Resonance, 2D Nutation Spectroscopy, Electric Field Gradient Tensor 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0153.pdf 
 Identifier    ZNA-1999-54a-0153 
 Volume    54 
6Author    J. L. Schiano, A. J. Blauch, M. D. GinsbergRequires cookie*
 Title    Optimization of NQR Pulse Parameters using Feedback Control  
 Abstract    A new method for increasing the probability of detecting nuclear resonance signals is demon-strated experimentally. It is well known that the detection of signals with a low signal to noise ratio (SNR) results in missed detections of false alarms. In situations where the noise is correlated or where limited data is averaging, it may not be possible to achieve a desired SNR through averaging alone. We present an alternative approach in which a feedback algorithm automatically adjusts pulse parameters so that the SNR and probability of correct detection are increased. Experimental results are presented for the detection of 14 N NQR signals. 
  Reference    Z. Naturforsch. 55a, 67—73 (2000); received August 28 1999 
  Published    2000 
  Keywords    Nuclear Quadrupole Resonance, Feedback Control, Receiver Operating Characteristics 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0067.pdf 
 Identifier    ZNA-2000-55a-0067 
 Volume    55 
7Author    Taro Eguchi, Koichi Mano, Nobuo NakamuraRequires cookie*
 Title     
 Abstract    p p lic a tio n o f M a x im u m E n tro p y M e th o d (M E M) f o r P r e c is e D e te r m in a tio n o f N Q R F re q u e n c ie s The maximum entropy method (MEM) is applied to the analysis of the closely spaced nuclear quadrupole resonance spectra of 35C1 in hexachlorobenzene and 14N in frarts-azobenzene. The superiority of the MEM to usual FFT spectra is discussed with respect to the precision of frequency measurements and the noise characteristics in broad and noisy NQR spectra. 
  Reference    Z. Naturforsch. 44a, 15—18 (1989); received November 3 1988 
  Published    1989 
  Keywords    Maximum Entropy Method, Nuclear Quadrupole Resonance, Phase Transition, Spec­ tral Analysis 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-0015.pdf 
 Identifier    ZNA-1989-44a-0015 
 Volume    44 
8Author    VirendraK. Sharma, Werner Richarz, Surendra Sharma, Alarich WeissRequires 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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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0545.pdf 
 Identifier    ZNA-1990-45a-0545 
 Volume    45 
9Author    Makoto Kaga, Piotr Koziol, Tetsuo Asaji, Daiyu NakamuraRequires cookie*
 Title    Electric field Gradient Modulation by Motion of Lone-Pair Electrons in [(CH 3 ) 3 S] 2 MC1 6 (M = Pt, Sn) as a Possible Relaxation Mechanism of Chlorine Nuclear Quadrupole Resonance  
 Abstract    The temperature dependence of the chlorine NQR spin-lattice relaxation time T^was observed for trimethylsulfonium hexachlorometallates(IV), [(CH 3) 3 S] 2 MC1 6 (M = Pt, Sn), trimethylammonium hexachlorostannate(IV), [(CH 3) 3 NH] 2 SnCl 6 , and tetramethylphosphonium hexachlorostannate(IV), [(CH 3) 4 P] 2 SnCl 6 . The quadrupolar relaxation in [(CH 3) 3 NH] 2 SnCl 6 and [(CH 3) 4 P] 2 SnCl 6 can be described by the usual librational and reorientational motion of the complex anion at lower and higher temperatures, respectively. Besides T 1Q due to these two mechanisms, T 1Q minimum was observed at ca. 90 and 120 K for [(CH 3) 3 S] 2 PtCl 6 and [(CH 3) 3 S] 2 SnCl 6 , respectively, which is attributable to the electric field gradient modulation by the motion of the [(CH 3) 3 S] + cation having lone-pair electrons. The activation energies for the isotropic reorientation of the complex anion were determined as46,65, 59, and 60 kJ mol^ for [(CH 3) 4 P] 2 SnCl 6 , [(CH 3) 3 NH] 2 SnCl 6 , [(CH 3) 3 S] 2 PtCl 6 , and [(CH 3) 3 S] 2 SnCl 6 , respectively. 
  Reference    Z. Naturforsch. 45a, 1033—1037 (1990); received May 26 1990 
  Published    1990 
  Keywords    Nuclear Quadrupole Resonance, Spin-Lattice Relaxation, EFG Modulation, Lone-Pair Electrons 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-1033.pdf 
 Identifier    ZNA-1990-45a-1033 
 Volume    45 
10Author    O. Ege, S. Nishijima, E. Kimura, H. Akiyama, S. Hamai, H. NegitaRequires cookie*
 Title    Powder Zeeman NQR Study on the Absorption Forms for Nuclear Spin 5/2  
 Abstract    For nuclei which have a nuclear spin of 5/2 and exhibit a small asymmetry parameter of the electric field gradient (77) at the nuclear site, line shapes of the Powder Zeeman NQR (PZNQR) spectra based on the transition between the energy levels m x = ± 1/2 and ± 3/2 (the lower frequency line) were stud-ied by means of computer simulations and experiments, (i) When an 77 value is very small (type 1; 77 = 0), the line shape exhibits two shoulders like the style of the American football player, (ii) While an 77 value is small (type 2; 0< 77 < around 0.01) but not zero, the line shape has two small peaks which are symmetrically located on the shoulders, as in the case of the small 77 type of spin 3/2. (iii) When an 77 value is not small (type 3; around 0.01 <77), the line shape has two symmetrical dips in stead of the peaks, which are also similar to the case of not small 77 type of spin 3/2. As the 77 value increases from around 0.01, the two dips grow and reach the maximum at the 77 value of 0.349, and then become small-er and obscure in the range of 77 larger than 0.349. __ The observations of PZNQR spectra were performed for several compounds including the ,27 I and/or 12 'Sb nuclei to estimate the 77 values, and gave the results as follows: very small for I (207.683 and 209.133 MHz, at 77 K) in Snl 4 ; very small for 127 I (176.496 and 177.438 MHz, at 77 K) in Gal 3 ; small for 127 I (265.102 MHz, at 77 K) in CH 3 I; 0.33 for 127 I (247.69 MHz, at 77 K) in C 2 H 5 I; 0.27 for 121 Sb (58.23 MHz, at 290 K) in SbCl 3 . The estimated 77 values were compared to those obtained from the fre-quencies of two NQR lines for spin 5/2. They were in good agreement with each other for the small re-gion of 77, though somewhat large disagreements were seen in the cases of not small 77 values. 
  Reference    Z. Naturforsch. 53a, 314—317 (1998); received March 24 1998 
  Published    1998 
  Keywords    NQR, Nuclear Quadrupole Resonance, Zeeman effect, Powder Zeeman NQR, Spin 5/2 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0314.pdf 
 Identifier    ZNA-1998-53a-0314 
 Volume    53 
11Author    J. L. Schiano, M. D. GinsbergRequires cookie*
 Title    A Pulsed Spectrometer Designed for Feedback NQR  
 Abstract    A pulsed NQR spectrometer specifically designed to facilitate real-time tuning of pulse sequence parameters is described. A modular approach based on the interconnection of several rack-mounted blocks provides easy access to all spectrometer signals and simplifies the task of modifying the spectrometer design. We also present experimental data that demonstrates the ability of the spectrometer to increase the signal to noise ratio of NQR measurements by automatically adjusting the pulse width in the strong off-resonant comb pulse sequence. 
  Reference    Z. Naturforsch. 55a, 61—66 (2000); received August 28 1999 
  Published    2000 
  Keywords    Nuclear Quadrupole Resonance, Spectrometer Design, Real-time Programmable Pulse Sequence Generator 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0061.pdf 
 Identifier    ZNA-2000-55a-0061 
 Volume    55 
12Author    Keizo Horiuchi, Daiyu NakamuraRequires cookie*
 Title    Chlorine Nuclear Spin-Spin Relaxation Mechanism in Mg(H 2 0) 6 SnCl 6 as Studied by NQR and NMR Techniques  
 Abstract    The 35 C1 NQR spin-lattice relaxation time T1Q, spin-spin-relaxation time T2Q, and J H NMR spin-lattice relaxation time in the rotating frame T le in Mg(H20)6SnCl6 were measured as functions of temperature. Above room temperature T2q increased rapidly with increasing temperature, which can be explained by fluctuations of the local magnetic field at the chlorine nuclei due to cationic motions. From the T le experiments, these motions are found to be attributable to uniaxial and overall reorientations of [Mg(H20)6] 2+ ions with activation energies of 95 and 116 kJ mol -1 , respectively. Above ca. 350 K, T1Q decreased rapidly with increasing temperature, which indicates a reorientational motion of [SnCl6] 2-ions with an activation energy of 115 kJ mol -1 . 
  Reference    Z. Naturforsch. 47a, 277—282 (1992); received October 29 1991 
  Published    1992 
  Keywords    Complex compounds, Molecular dynamics, Nuclear relaxation, Nuclear quadrupole resonance, Nuclear magnetic resonance 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0277.pdf 
 Identifier    ZNA-1992-47a-0277 
 Volume    47 
13Author    Masahiko Suhara, Koichi ManoRequires cookie*
 Title    NQR and Phase Transitions in Hexachlorocyclopropane Crystal  
 Abstract    35 C1 NQR and DSC studies on phase transitions in hexachlorocyclopropane (HCCP), C 3 C1 6 , are reported. It is found that HCCP has three solid phases: A high temperature disordered phase (Phase I) above 301 K (no NQR spectrum was observed); a metastable phase (Phase II), which exhibited 6 NQR lines from 77 to 270 K; a low temperature phase (Phase III) in which a 24-multiplet of 35 C1 NQR lines at 77 K, the most complex multiplet spectrum ever reported was observed. DSC measurement shows a A-type transition at 301 K and a broad transition of very slow rate at 285 K. The structure and mechanism of phase transitions in HCCP crystal are discussed. 
  Reference    Z. Naturforsch. 45a, 339—342 (1990); received August 23 1989 
  Published    1990 
  Keywords    Nuclear quadrupole resonance, Phase transition, Crystal structure, Differential scan-ning calonmetry, Order-disorder transition 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0339.pdf 
 Identifier    ZNA-1990-45a-0339 
 Volume    45 
14Author    M. Tei, H. Takai, K. Mizoguchi, K. KumeRequires cookie*
 Title    Cu NQR Study on Transverse Relaxation Rate below T c in YBa 2 Cu 3 0 7  
 Abstract    The transverse relaxation rate T 2 l was measured in YBa 2 Cu 3 0 7 from 4.2 to 100 K in zero magnetic field. It showed a sudden drop just below T c down to 1/3 of that above T c . A cusp-shaped sharp peak of Tf 1 was found at 35 K for Cu(2) (plane) site, but not for Cu(l) (chain) site. Except the peak, all the behavior can be interpreted by the model of Pennington et al. that the origin of T 2 1 at 100 K is mainly the local field fluctuation by the Cu d-electron and secondly the indirect nuclear spin-spin coupling via superexchange interaction between Cu-ions. Below T c the former is sup-pressed. 
  Reference    Z. Naturforsch. 45a, 429—432 (1990); received August 22 1989 in revised form October 30 1989 
  Published    1990 
  Keywords    Nuclear quadrupole resonance, High T c superconductor, Transverse relaxation rate, Super-exchange interaction, Electron spin fluctuation 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0429.pdf 
 Identifier    ZNA-1990-45a-0429 
 Volume    45 
15Author    Gary Wulfsberg, Debra Jackson, William Ilsley, Shi-Qi Dou, Alarich Weiss, John GagliardiRequires cookie*
 Title    Coordination of OrfÄö-Chlorines in Copper (I) and Silver (I) 2,6-Di-and 2,4,6-Trichlorophenolates Crystal Structure of (2,4,6 -Trichlorophenolato-O, CI) bis (triphenylphosphine) silver (I)  
 Abstract    The crystal structure of (Ph 3 P) 2 AgOC 6 H 2 Cl 3 (I) is reported along with the syntheses and 35 C1 and 63 Cu NQR spectra of I and several related silver (I) and copper (I) 2,6-di-and 2,4,6-trichlorophe-nolates containing phosphines, phosphites, and pyridine as co-ligands. I crystallizes in space group P2 Jc with a= 16.692(4) Ä, b= 17.942 (4) A, c= 12.857 (3) Ä, /? = 97.60 (1)°, F = 3816.68 Ä 3 , and Z = 4. The final R (F) = 0.0475 and R (W) = 0.0396. Ag is coordinated in a trigonal planar geometry by the P atoms of the two triphenylphosphine ligands and the O atom of the chlorophenolate; Ag is then capped by one ortho-chlorine of the trichlorophenolate ligand at a distance of 3.160 (2) Ä. In the 35 C1 NQR spectrum of this compound the two orf/io-chlorines of the trichlorophenolate ligand have a large frequency difference of 1.500 MHz, indicating that one ortho-chlorine is coordinated to the silver; 35 C1 NQR spectra of related complexes are also presented and discussed. The 35 C1 NQR frequency differences of coordinated and non-coordinated orr/io-chlorines in metal chlorophenolates correlate well with the metal-chlorine distances but not with the metal-chlorine-carbon bond angles. A different correlation is found for the silver complexes of dichloroalkanes; possible reasons for this are discussed. 
  Reference    Z. Naturforsch. 47a, 75—84 (1992); received July 15 1991 
  Published    1992 
  Keywords    Nuclear quadrupole resonance, Chlorophenolates, Crystal structure, Chlorocarbons as ligands, Silver(I) complexes 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0075.pdf 
 Identifier    ZNA-1992-47a-0075 
 Volume    47 
16Author    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 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0713.pdf 
 Identifier    ZNA-1992-47a-0713 
 Volume    47 
17Author    J. Pelzl, C. DimitropoulosRequires cookie*
 Title      
 Abstract    Recent and novel data obtained from chlorine NQR measurements on natural and deuterated (NH4)2 MC16 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 NOR frequency \ q and relaxation rates Tj-1 , T2-1 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 vQ and Tt~ 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 rel. The observed divergence of Tl_ 1 at the transition point can be described in terms of a spin-phonon process in the presence of an overdamped soft mode. Deuteration of (N H 4)2 TeCl6 only slightly affects the transition of Tcl but leads to new structural changes at lower temperatures. Whereas the natural compound stays trigonal down to 4.2 K the deuterated crystal undergoes two additional structural transformations at Te 2 = 48 K and Tc3 = 28 K which are correlated with a slowing down of the deuteron motion. Approaching Tc2 from above, the spin-lattice relaxation rate and the spin-spin relaxation rate of the chlorine NQR exhibit distinct anomalies which are attributed to limited jumps of the octahedron in a shallow potential. The barrier height of this potential deduced from the chlorine NQR spin-lattice relaxation rate is 400 K. The transition at Tc2 is explained by the condensation in one minimum of this potential. At Tc3 a long range correlation is formed which is accompanied by a rotation of the octahedron about its fourfold axis. A similar mechanism is adopted for the transitions observed in (NH4)2 SeCl6 at Tc= 24 K and in (ND4)2 SeCl6 at Tc = 48 K. 
  Reference    Z. Naturforsch. 49a, 232—246 (1994); received August 12 1993 
  Published    1994 
  Keywords    Nuclear quadrupole resonance, Structural phase transitions, Ammonium-ion dynam­ ics, Hexahalogenometallates, Critical behaviour 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0232.pdf 
 Identifier    ZNA-1994-49a-0232 
 Volume    49 
18Author    Mariusz Maćkowiak, Piotr KątowskiRequires cookie*
 Title    2D Off-Resonance Nutation NQR Spectroscopy of Spin 3/2 Nuclei  
 Abstract    The effects of off-resonance irradiation in nutation NQR experiments are demonstrated both experimentally and theoretically. The theoretical description of the off-resonance effects in 2D nutation NQR spectroscopy is given, and general exact formulas for the asymmetry parameter are obtained. It is shown that the outcome of the off-resonance nutation experiments depends on the data acquisition procedure, leading to one-or three-line nutation spectra. To explain this fact and to describe the off-resonance nutation experiment properly, the transient response theory of a quadrupolar spin system to an RF pulse was modified using the wave-function approach. The 2D separation of interactions technique has been applied to separate a static and a randomly time-fluctuating dynamic part of the quadrupole interaction in the antiferroelectric phase of poly-crystalline ammonium dihydrogen arsenate. Two-dimensional off-resonance nutation NQR spectroscopy has been used to determine the full quadrupolar tensor of spin-3/2 nuclei in several molecular crystals containing the 35 C1 and 75 As nuclei. The off-resonance phenomena in 2D NQR are very important from the practical point of view (determination of r\ in multiple or broad-line spectrum) and also provide interesting information on the dynamic properties of a quadrupolar spin system. 
  Reference    Z. Naturforsch. 53a, 285—292 (1998); received January 26 1998 
  Published    1998 
  Keywords    Nuclear Quadrupole Resonance, 2D Nutation Spectroscopy, Off-resonance Irradiation, Electric Field Gradient Tensor 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0285.pdf 
 Identifier    ZNA-1998-53a-0285 
 Volume    53 
19Author    P. F. Meier, T. A. Claxton, P. Hüsser, S. Plibersek, E. P. StollRequires cookie*
 Title    Cluster Calculations of Hyperfine Interactions in Superconducting Copper Compounds  
 Abstract    This paper discusses first-principles cluster investigations on the electronic structure of YBa2Cu3Ü7 and La2CuC>4 performed at the University of Zürich. In particular, electric field gradients have been calculated at the copper sites and their dependence on applying uniaxial strain is studied. Magnetic hyperfine interactions have been evaluated from spin-polarized calculations, and the transfer of spin density from neighboring copper ions is explained. An interpretation is given of the nuclear quadrupole resonance spectra in doped La2CuC>4. 
  Reference    Z. Naturforsch. 55a, 247—255 (2000); received August 26 1999 
  Published    2000 
  Keywords    Cluster Calculations, Electric Field Gradients, High-Temperature Superconductors, Hyperfine Fields, Nuclear Quadrupole Resonance 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0247.pdf 
 Identifier    ZNA-2000-55a-0247 
 Volume    55