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1996 (1)
1992 (1)
1Author    T. Radnai, H. OhtakiRequires cookie*
 Title    Intramolecular and Liquid Structures of Tetramethylurea Studied by Means of X-Ray Diffraction  
 Abstract    The intramolecular and liquid structures of tetramethylurea (TMU) were investigated by the liquid x-ray diffraction method. It is confirmed that in the liquid state the four methyl groups are out of the plane which is constructed by the O, C, and the two N atoms, the molecular structure being similar to what had been found in the gas phase. All structural parameters are in good agreement with those of TMU determined in the gas phase and with those of amide derivatives in the liquid phase. The liquid is characterized by a random distribution of molecules as predominant, but a weak molecular ordering characterized by approximately two intermolecular nonbonding Me • • • O dis-tances at 340 pm is proposed. 
  Reference    Z. Naturforsch. 47a, 1003—1010 (1992); received May 20 1992 
  Published    1992 
  Keywords    Tetramethylurea, Liquid x-ray diffraction, Liquid structure, Molecular structure, Non-aqueous solvent 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-1003.pdf 
 Identifier    ZNA-1992-47a-1003 
 Volume    47 
2Author    W. J. Bresser, J. Wells, M. Zhang, P. BoolchandRequires cookie*
 Title    Molecular Origin of Glass Forming Tendency in Ternary Te-Se-Br(Cl) Chalcohalide Glasses  
 Abstract    Bulk glasses of Te 3 _-Se-(CI or Br) 2+V , the composition spanning the glass forming range, were characterized by differential scanning calorimetry, l2r, Te absorption, and 129 I emission Mössbauer spectroscopy. The results reveal that the stoichiometric glasses Te 3 (Cl or Br) 2 consists of c-Te 3 Cl 2 -like chain fragments about 1.5 nm long and terminated by one-fold coordinated halogen atoms. The 12:i Te electric hyperfine structure results reveal that Te replacement by Se (z =/ 0) leads to preferential occupancy at those Te sites in the chains that are two-fold coordinated, and in a rather striking fashion demonstrate that the average length of the chain fragments remains independent of Se concentration. Halogen atoms in the glasses act as chain terminators, and also bond to Te-sites in the chains to produce four-fold coordinated sites. The low glass transition temperatures (7g ~ 70 -90°C), the low average coordination number of the proposed chain-fragments, along with the hyperfine structure results, suggest that the extensive glass forming tendency in the chalcohalides derives from the floppiness of the chain-fragments. 
  Reference    Z. Naturforsch. 51a, 373—380 (1996); received January 5 1996 
  Published    1996 
  Keywords    ^Te Absorption Mössbauer Spectroscopy, 129 I Emission Mössbauer Spectroscopy, Chalcohalide Glasses, Molecular Structure, Glass Formation 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0373.pdf 
 Identifier    ZNA-1996-51a-0373 
 Volume    51