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'Phase transitions' in keywords Facet   Publication Year 1991  [X]
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1991[X]
1Author    Z. Szafrańska, A. Pająk, KozakRequires cookie*
 Title     
 Abstract    Proton and fluorine NMR second moments and spin-lattice relaxation times for polycrystalline tetrabutylammonium tetrafluoroborate have been measured over a wide range of temperatures at several Larmor frequencies. An analysis of cross-relaxation effects results in a determination of activation parameters for anion and cation reorientations. Three solid phases characterized by different ion dynamics are evidenced. M o le c u la r M o tio n in S o lid T e tra b u ty la m m o n iu m T e tr a f lu o r o b o r a te 
  Reference    Z. Naturforsch. 46a, 545—550 (1991); received March 14 1991 
  Published    1991 
  Keywords    NMR, Cross-relaxation, Molecular motions, Phase transitions 
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 TEI-XML for    default:Reihe_A/46/ZNA-1991-46a-0545.pdf 
 Identifier    ZNA-1991-46a-0545 
 Volume    46 
2Author    MarcoL H Gruwel1, RoderickE. WasylishenRequires cookie*
 Title     
 Abstract    e u te riu m N M R S tu d y o f th e S o lid -S o lid P h a s e T ra n s itio n in P h e n e th y la m m o n iu m B ro m id e 30, 1991 Using 2H NMR, the dynamics of the cation in phenethylammonium bromide were studied in the two solid phases. Line shape and spin-lattice relaxation rate studies of the ammonium headgroups and the adajacent methylene groups indicate the onset of alkyl-chain motion prior to the first order phase transition. In the low-temperature phase the line shape and the spin-lattice relaxation rates of the -ND3 groups are consistent with C3 jumps and an activation energy of 54±4 kJ mol"1. However, in the high-temperature phase the spin-lattice relaxation studies indicate the presence of small-angle diffusion of the -ND3 groups around the C3 symmetry axis. In this phase the -CD2-groups show line shapes typical of large-amplitude two-site jumps occurring at a rate > 107 s~ l. In the low-temperature phase, at temperatures below 295 K, the -CD2-2H NMR line shapes indicate that the C-D bonds are essentially static. 
  Reference    Z. Naturforsch. 46a, 691 (1991); received March 
  Published    1991 
  Keywords    2H NMR, Phase transition, Relaxation, Molecular jumps 
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 TEI-XML for    default:Reihe_A/46/ZNA-1991-46a-0691.pdf 
 Identifier    ZNA-1991-46a-0691 
 Volume    46