| | 1 | 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 | |
| 2 | Author
| Makoto Kaga, Piotr Koziol, Tetsuo Asaji, Daiyu Nakamura | Requires 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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| default:Reihe_A/45/ZNA-1990-45a-1033.pdf | | | | Identifier
| ZNA-1990-45a-1033 | | | | Volume
| 45 | |
| 3 | Author
| Masahiko Suhara, Koichi Mano | Requires 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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| default:Reihe_A/45/ZNA-1990-45a-0339.pdf | | | | Identifier
| ZNA-1990-45a-0339 | | | | Volume
| 45 | |
| 4 | Author
| M. Tei, H. Takai, K. Mizoguchi, K. Kume | Requires 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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| default:Reihe_A/45/ZNA-1990-45a-0429.pdf | | | | Identifier
| ZNA-1990-45a-0429 | | | | Volume
| 45 | |
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