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'Electron Spin Resonance' in keywords Facet   Publication Year 1989  [X]
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1Author    Robert Schupfner, Adolf MüllerRequires cookie*
 Title    Temperature-Dependent ESR Studies of Radical Pairs in Single Crystals of Barbituric Acid  
 Abstract    After irradiation o f single crystals o f barbituric acid with X-rays at 77 K different types of radical pairs are found, which are com posed o f only one type of monoradical. The properties of radical pairs o f the unpaired electrons are studied using frequency-variable ESR m ethods at various temperatures. In addition to the radical pairs A D and BC two further pairs A 'D ' and X Y were identified. M easurem ents o f the fine structure parameter D showed a linear temperature dependence in som e regions betw een 77 K and 290 K. At 240 K the radical pairs A D and A 'D ' changed reversibly into A *D * and this pair remained stable up to 290 K. A level anticrossing effect was observed with the pair A D . The exchange energy J between the singlet state and the triplet state was determ ined as —(15.1 ± 0.6) GHz at 77 K and its tem pera­ ture coefficient as —(3.8 ± 0.8) x 10"3K '. 
  Reference    Z. Naturforsch. 44c, 849 (1989); received April 20/June 29 1989 
  Published    1989 
  Keywords    Barbituric A cid Single Crystals Radical Pairs, Electron Spin Resonance, Level Anticrossing 
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 TEI-XML for    default:Reihe_C/44/ZNC-1989-44c-0849.pdf 
 Identifier    ZNC-1989-44c-0849 
 Volume    44