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2000 (2)
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1Author    T. SpringerRequires cookie*
 Title    High-Resolution Neutron Spectroscopy for the Investigation of Hydrogen Diffusion and Molecular Rotations in Solids  
 Abstract    An introductory survey on applications of high-resolution neutron spectroscopy is presented, dealing with the motion of hydrogen in solids, namely concerning (i) random rotational motions or stationary tunneling states of NH 4 -ions or CH 3 -groups, and (ii) diffusion of hydrogen in alloys. For the rotation of hydrogenous groups in solids, at higher temperatures rotational jumps can be found, whereas quantum states are observed by |J.eV-spectroscopy at temperatures below 50 K. On the other hand, hydrogen diffusion does not reveal pronounced evidence of quantum effects, except for hydrogen in a metal containing impurity atoms. 
  Reference    Z. Naturforsch. 48a, 406—414 (1993); received January 7 1992 
  Published    1993 
  Keywords    Quasielastic neutron scattering, Diffusion, Tunneling 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0406.pdf 
 Identifier    ZNA-1993-48a-0406 
 Volume    48 
2Author    Julio Maranon, OscarM. SorarrainRequires cookie*
 Title    Polarization, Isopotential Maps and Tunneling in Guanine, Cytosine, and Tautomeric Forms  
 Abstract    We have used the CNDO/2-CI method to calculate the isopotential maps for the fundamental state and the direction of the polarizations corresponding to several singlet transitions in the mole­ cules of guanine, cytosine and tautomeric forms. We have also calculated the times for proton tunneling and equilibrium constants between both conformers corresponding to the fundamental and some excited states. The results have been compared with the available experimental data. 
  Reference    Z. Naturforsch. 33c, 23 (1978); received November 2 1977 
  Published    1978 
  Keywords    Polarization, Isopotential, Tunneling, Guanine, Cytosine 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0023.pdf 
 Identifier    ZNC-1978-33c-0023 
 Volume    33 
3Author    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 
4Author    Taka-Aki Nihei, Shin'. Ichi, Ishimaru, Ryuichi IkedaRequires cookie*
 Title    C1 NQR Studies of Hydrogen Transfer in Crystalline /7-Chlorobenzoic Acid  
 Abstract    35 C1 NQR frequencies and spin-lattice relaxation times 7, Q were measured inp-ClC 6 H 4 C0 2 H(PCB A) and p-ClQF^CC^DtPCBA-d,) at 77-333 K. T lQ in PCB A gave a shallow minimum of 8.0 ms at ca. 110 K, which could be explained by a double proton transfer mechanism in the carboxylic acid dimer referring to *H NMR data giving a T 1H minimum at almost the same temperature. PCBA-d, showed temperature dependent NQR frequencies quite analogous to those in PCBA, whereas their r 1Q behavi-our was quite different in its minimum value and its temperature as well as temperature gradient. These results were explained by suppressed deuteron tunnelling and the Ubbelohde effect. 
  Reference    Z. Naturforsch. 55a, 355—358 (2000); received August 27 1999 
  Published    2000 
  Keywords    CI NQR, Hydrogen-Bond, Hydrogen-transfer, Tunneling 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0355.pdf 
 Identifier    ZNA-2000-55a-0355 
 Volume    55