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'NMR' in keywords Facet   Publication Year 1997  [X]
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1997[X]
1Author    M. Grottel, M. Szafrański, Z. PająkRequires cookie*
 Title    NMR Study of Cation Motion in Guanidinium Iodoplumbates  
 Abstract    Proton NMR second moments and spin-lattice relaxation times of polycrystalline C(NH 2) 3 PbI 3 and [C(NH 2) 3 ]2PbI 4 were studied in a wide temperature range. The order-disorder character of the existing solid-solid phase transitions was confirmed and for tetraiodoplumbate a new phase transition at 170 K was discovered. For both compounds a dynamical inequivalence and unusual high mobility of the guanidinium cations were revealed. For the reorientations discovered (NH 2 group flipping, C 3 in-plane reorientation and a tumbling) the activation parameters were determined. 
  Reference    Z. Naturforsch. 52a, 783—788 (1997); received October 6 1997 
  Published    1997 
  Keywords    NMR, Molecular Motions, Phase Transitions 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0783.pdf 
 Identifier    ZNA-1997-52a-0783 
 Volume    52 
2Author    Roman GocRequires cookie*
 Title    Calculation of the NMR Second Moment for Solid Benzene with Rotation and Diffusion of Molecules -Numerical Approach  
 Abstract    Numerical calculations of the NMR second moment in case of rotation and diffusion of molecules were performed. As an example computer simulations of molecular reorientation and self-diffusion in solid benzene have been performed. For each model and rate of motion the Van Vleck's second moment of the proton NMR absorption spectrum was calculated, and these values were compared with experimental data. It is concluded that restricted self-diffusion must be implied in order to obtain better agreement between calculated and experimental NMR second moments. The temperature at which self-diffusion was detected through NMR line-width narrowing was found to be about 120 K, nearly 80 K less than the temperature at which the self-diffusion was detected by T lp relaxation measurements. 
  Reference    Z. Naturforsch. 52a, 477—184 (1997); received March 29 1997 
  Published    1997 
  Keywords    NMR, molecular rotation, self-diffusion, numerical approach 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0477.pdf 
 Identifier    ZNA-1997-52a-0477 
 Volume    52 
3Author    Roman Goc, JanW. WąsickiRequires cookie*
 Title    Computer Simulation of the Order-Disorder Transition in Ammonium Chloride  
 Abstract    The phase transition at T c = 243 K in ammonium chloride is well established to be of the order-disorder type. The ammonium chloride has a CsCl-type cubic structure with hydrogen atoms pointing toward four of the eight chloride ions at the corners of the unit cell. This means that there are two possible orientations of ammonium tetrahedron; a and b. In the ordered phase below the T c temperature all ammonium ions have the same, let it be a, orientation. Above the T c temperature ions are randomly distributed among the two possible orientations a and b. An attempt was made to correlate such structural transition with the second moment of the proton NMR absorption line. This approach was chosen because the second moment is the parameter of the NMR line for which the exact theoretical formula exist, and which is mainly a function of the structure and the reorien-tational state of the studied material. It was found that the NMR second moments calculated for the described above model of the structural transition properly reflect the changes of the experimental NMR second moments measured at temperatures below and above this transition. 
  Reference    Z. Naturforsch. 52a, 609—613 (1997); received June 18 1997 
  Published    1997 
  Keywords    NMR, Ammonium chloride, Phase transition, Simulation 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0609.pdf 
 Identifier    ZNA-1997-52a-0609 
 Volume    52 
4Author    J. Seliger, V. ŽagarRequires cookie*
 Title    A New Nuclear-Quadrupole Double-Resonance Technique based on Solid Effect  
 Abstract    A new nuclear-quadrupole double-resonance technique is described. It has a higher sensitivity and a higher resolution than the conventional nuclear-quadrupole double-resonance technique based on solid effect. The new technique involves magnetic field cycling between a high and a low static magnetic field and simultaneous application of two //magnetic fields when the sample is in the low static magnetic field. A strong rf magnetic field induces "forbidden" simultaneous transitions in a magnetic (usually 1 H) and in a quadrupole spin system and thus couples the two spin systems. A weak//magnetic field induces transitions between the energy levels of the quadrupole nuclei and simulates a fast spin-lattice relaxation of the quadrupole nuclei when its frequency matches an NQR frequency. The sensitivity and resolution of the new technique are discussed and test measurements in tris-sarcosine calcium chloride are presented. 
  Reference    Z. Naturforsch. 52a, 337—342 (1997); received October 9 1996 
  Published    1997 
  Keywords    NQR, NMR, Double Resonance, Magnetic Field Cycling, Solid Effect 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0337.pdf 
 Identifier    ZNA-1997-52a-0337 
 Volume    52