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'Isotope effects' in keywords Facet   section ZfN Section A  [X]
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1Author    Tetsuo Asaji, Tomohiro IshizakaRequires cookie*
 Title    Effect of Deuteration on Ammonium Motion and Structural Phase Transition Studied by Nuclear Quadrupole Resonance  
 Abstract    35 C1 NQR measurements revealed two phase transitions at 14.5 K and 70 K in NH4ICI4. By deuteration of the ammonium ions, the respective transition temperature increased to 27 K and 74 K. In the lowest-temperature phase of NH4ICI4, by the deuteration a remarkable change of the temperature dependence of the 35 C1 NQR frequencies was observed. The NQR spin-lattice relaxation-time minimum, ascribable to the modulation effect of the electric field gradient (EFG) due to a motion of the ammonium ions, was observed at 7 K and 11 K in NH4ICI4 and ND4ICI4, respectively. The activation energy of the ammonium motion and the fluctuation fraction q /q of the EFG were determined to be 0.32 kJ moP 1 and 1.3xlO~ 3 for NH4ICI4, and 0.30 kJ mol -1 and 0.88xl0~ 3 for ND4ICI4. The experimental result suggests that the inter-ionic interaction between the ammonium ion and the ICl^ complex anion is weakened by the deuteration. However, the frequency shift observed in the lowest-temperature phase is much larger in ND4ICI4 than in NH4ICI4. This suggests that the lattice distortion in NH4ICI4 is suppressed to a great deal by the tunneling rotation of NH4 ions. The effective inter-ionic interaction responsible for the lattice distortion, the transition temperature and the enhancement of tunneling of NH4 as compared with ND4 is discussed for NH4ICI4 as well as for previously reported NH4AUCI4 and ct-N^HgCb. 
  Reference    Z. Naturforsch. 55a, 83—89 (2000); received August 26 1999 
  Published    2000 
  Keywords    Isotope Effect, Tunneling, Phase Transition, Ammonium, NQR 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0083.pdf 
 Identifier    ZNA-2000-55a-0083 
 Volume    55 
2Author    Morikazu Hosoe, Takao Oi, Tadashi Nagumo, Hidetake KakihanaRequires cookie*
 Title    Rubidium Isotope Separation by Constant Current Electromigration in a Cation-exchange Membrane  
 Abstract    Separation of rubidium isotopes (85 Rb, 87 Rb) by electromigration in a cation exchange mem-brane has successfully been carried out in a band operation manner at 25 °C. The migration velocity has been varied from 2.5 to 12.1 cm/h. There existed a wide non-isotope-fractionated zone between the 85 Rb enriched zone at the front and the 85 Rb depleted zone at the rear of the band. The single stage separation factor was about 1.0009 and was independent of the migration velocity, migration length and operation technique at a given temperature. The steepness of the 85 Rb accumulation curves, increased with increasing migration velocity. 
  Reference    Z. Naturforsch. 42a, 606—610 (1987); received March 5 1987 
  Published    1987 
  Keywords    Isotope separation, isotope effect, electromigration, rubidium isotope, ion-exchange membrane 
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 TEI-XML for    default:Reihe_A/42/ZNA-1987-42a-0606.pdf 
 Identifier    ZNA-1987-42a-0606 
 Volume    42 
3Author    L. Xie, W. H. SaundersRequires cookie*
 Title    Is  
 Abstract    o to p e E ffe c ts in K in e tic E n o la te F o r m a tio n fro m 2 -P e n ta n o n e a n d 2 -P e n t a n o n e -l , l , l -d 3 This paper is dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday 2-Pentanone and 2-pentanone-l,l,l-d3 were treated with three-fold excesses of lithium diiso-propylamide (LDA) or lithium hexamethyldisilazide (LHMDS) in tetrahydrofuran (THF) with and without hexamethylphosphoric triamide (HMPA, 3 mol per mol of base) at temperatures ranging from 24 to — 70 °C. The deuterium kinetic isotope effects calculated from the product ratios (mea­ sured by GLC as trimethylsilyl enol ethers) showed a range of temperature dependences: none (LDA in THF), attenuated with A^jA^ = 2.53 (LHMDS in THF), and normal with /1H//1D~0.6 indicating moderate tunneling (LDA and LHMDS in THF-HMPA). The variation in temperature dependence is attributed to reaction via multiple base species in which HMPA affects the equilibria between the base species. 
  Reference    Z. Naturforsch. 44a, 413 (1989); received January 13 1989 
  Published    1989 
  Keywords    Isotope Effects, Kinetic Enolates, Temperature Dependence, Lithium Dialkylamide Bases 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-0413.pdf 
 Identifier    ZNA-1989-44a-0413 
 Volume    44 
4Author    Peder Svensson, Nils-Äke Bergman, Per AhlbergRequires cookie*
 Title    Is A Theoretical Study using the Ab Initio STO -3G Potential Energy Surface  
 Abstract    o to p e E ffe c ts a n d C o n c e rte d T w o -H y d ro n -T r a n s f e r b e tw e e n F o rm a m id in e M o le c u le s Dedicated to Professor Jacob Bigeleisen on the occasion of his 70 th birthday With the intention to assist mechanistic studies of two-hydron-transfer reactions using lH/2H isotope effects we have carried out theoretical studies of the two-hydron-transfer reaction between formamidine molecules. The ab initio STO-3G potential energy surface has been calculated and all stationary points characterized by their force constant matrices. With this basis set the two hydrons are transferred concertedly and synchronously. The transition state (TS) has D2h symmetry. 'H/2H isotope effects were calculated using the Bebovib-IV program. Our results deviated from predictions made from common simple vibrational models. The isotope effects are dominated by the zero-point-energy contribution. The effect due to the stretching vibrations of the initial state is to a small extent counteracted by stretching of the TS. The bending vibrations appear to play a dominant role in reducing the magnitude of the isotope effect for the two-hydron-transfer reaction to a value expected for a one-hydron-transfer reaction. 
  Reference    Z. Naturforsch. 44a, 473—479 (1989); received May 18 1989 
  Published    1989 
  Keywords    Two-hydron-transfer, Formamidine, Ab initio, STO-3G, Isotope effects 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-0473.pdf 
 Identifier    ZNA-1989-44a-0473 
 Volume    44 
5Author    C. Herdlicka, J. Richter, M. D. ZeidlerRequires cookie*
 Title    Self-Diffusion in Molten Lithium Nitrate  
 Abstract    Self-diffusion coefficients of 7 Li + ions have been measured in molten LiN0 3 with several com-positions of 6 Li + and 7 Li + over a temperature range from 537 to 615 K. The NMR spin-echo method with pulsed field gradients was applied. It was found that the self-diffusion coefficient depends on the isotopic composition and shows a maximum at equimolar ratio. At temperatures above 600 K this behaviour disappears. 
  Reference    Z. Naturforsch. 47a, 1047—1050 (1992); received July 16 1992 
  Published    1992 
  Keywords    Molten salts, Self-diffusion, Isotope effect, NMR spin-echo 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-1047.pdf 
 Identifier    ZNA-1992-47a-1047 
 Volume    47 
6Author    Masahisa KakiuchiRequires cookie*
 Title    Hydrogen Isotope Fractionation in Aqueous Alkali Halide Solutions  
 Abstract    The D/H ratios of hydrogen gas in equilibrium with aqueous alkali halide solutions were deter-mined at 25 °C, using a hydrophobic platinum catalyst. The hydrogen isotope effect between the solution and pure water changes linearly with the molality of the solution at low concentrations, but deviates from this linearity at higher concentration for all alkali halide solutions. The magnitude of the hydrogen isotope effect is in the order; Kl > Nal > KBr > CsCl ^ NaBr > KCl > NaCl > LiCl, at concentrations up to a molality of 4 m. The sign and trend of the hydrogen isotope effect is different from that of oxygen. In aqueous alkali halide solutions, the hydrogen isotope effect is influenced by both the cation and the anion species, while the oxygen isotope effect is mainly caused by the cation species. This suggests that the mechanism of hydrogen isotope fractionation between the water molecules in the hydration spheres and the free water molecules differs from the mechanism of the oxygen isotope fractionation. The hydrogen and oxygen isotope effects for alkali halides, except LiCl and NaCl, may be influenced by changes in energy of the hydrogen bonding in free water molecules. 
  Reference    Z. Naturforsch. 52a, 811—820 (1997); received April 15 1997 
  Published    1997 
  Keywords    Hydrogen Isotope, Alkali halide, D/H fractionation, Thermodynamics, Isotope effect 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0811.pdf 
 Identifier    ZNA-1997-52a-0811 
 Volume    52 
7Author    Yoshio Kume, Tetsuo AsajiRequires cookie*
 Title    Chlorine-35 NQR Study of a Structural Phase Transition in (ND 4 ) 2 PdCV  
 Abstract    Temperature dependences of 35 C1 NQR frequencies and spin-lattice relaxation times were measured at 4.2 to 400 K for natural and deuterated ammonium hexachloropalladate. It was confirmed that only the deuterated salt undergoes a first order phase transition at 30 K. The crystal structure of the low-tem-perature phase is predicted to be the same as that of the deuterated ammonium hexachloroplatinate and hexachloroplumbate. The mechanism of the deuteration-induced phase transition is discussed. 
  Reference    Z. Naturforsch. 53a, 514—517 (1998); received March 24 1998 
  Published    1998 
  Keywords    Isotope Effect, Phase Transition, Chlorine NQR, Spin-lattice Relaxation, Deuterated Ammonium Hexachloropalladate 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0514.pdf 
 Identifier    ZNA-1998-53a-0514 
 Volume    53 
8Author    A. Kondoh, T. OiRequires cookie*
 Title    Interaction of Alkaline Earth Metal Ions with Acetic and Lactic Acid in Aqueous Solutions Studied by 13 C NMR Spectroscopy  
 Abstract    Interaction of alkaline earth metal (magnesium, calcium, strontium and barium) ions with acetic and lactic acid in aqueous media was investigated by 13 C NMR spectroscopy. In the acetate systems, signals whose chemical shifts were the averages of those of the free and bound acetate ions were observed. Downfield shifts of the carboxylate carbon signals with increasing metal ion concentration indicated that the acetate ion acted as a monodentate ligand coordinating to the metal ion using the carboxylate group. The metal ion concentration dependence of the peak positions of the methine and carboxylate carbon signals of the lactate ion in the lactate systems suggested that the lactate ion coordinated to a metal ion using the carboxylate and hydroxyl groups. Unique upfield shifts upon complexation in the magnesium lactate systems suggested that the lactate ion coordinated to the magnesium ion from outside the primary hydration sphere. The present results were consistent with the isotope effects of the alkaline earth metals observed in cation exchange chromatography. 
  Reference    Z. Naturforsch. 52a, 351—357 (1997); received December 4 1996 
  Published    1997 
  Keywords    13 C NMR, Alkaline Earth Metals, Acetic Acid, Lactic Acid, Isotope Effects 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0351.pdf 
 Identifier    ZNA-1997-52a-0351 
 Volume    52 
9Author    Y. Kume, T. A. Sajia, R. IkedaRequires cookie*
 Title    Low Temperature Isotope Effect in Ammonium Hexachloroselenate(IV) Studied by 35C1 NQR  
 Abstract    The temperature dependence o f the 35C1 N Q R frequency and spin-lattice relaxation time TlQ of (N H 4)2SeCl6 and (N D 4)2SeCl6 were measured from 400 K to 24.8 and 53.8 K, respectively. The disappearance of N Q R signals in the low temperature region of both salts is attributed to phase transitions. We concluded from the temperature behavior of just above the transition point that the operative mechanism o f the transition is different in these salts: The transition of (N D 4)2SeCl6 seems to be associated with rotary soft modes, while in the natural salt non-rotary soft modes seem to play an important role at the transition. 
  Reference    Z. Naturforsch. 49a, 297 (1994); received August 13 1993 
  Published    1994 
  Keywords    Isotope effect, Spin-lattice relaxation, N Q R, Phase transition, Ammonium hexa­ chloroselenate, Deuterated am m onium hexachloroselenate 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0297.pdf 
 Identifier    ZNA-1994-49a-0297 
 Volume    49