Molecular motion in ammonium hydrogendifluoride studied by pulsed NMR.
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概要
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The proton and fluorine-19 spin-lattice relaxation times, <I>T</I><SUB>1</SUB> and <I>T</I><SUB>1ρ</SUB>, in polycrystalline ammonium hydrogendifluoride were measured in the temperature range 142–345 K to elucidate the molecular motion of cation and anion. Below 200 K, the relaxation rates of both nuclei can be accounted for by dipolar interactions modulated <I>via</I> the isotropic reorientation of NH<SUB>4</SUB><SUP>+</SUP> ions. The log<I>T</I><SUB>1ρ</SUB> <I>versus</I> 1/<I>T</I> curves above 200 K exhibit two distinct minima, suggesting that two crystallographically nonequivalent HF<SUB>2</SUB><SUP>−</SUP> ions undergo 180°-flips about their two-fold axes with different correlation times. The activation energy of the NH<SUB>4</SUB><SUP>+</SUP> reorientation was determined to be 25.5±1.0 kJ/mol from the <I>T</I><SUB>1</SUB> data, while those of the 180°-flips were estimated from the <I>T</I><SUB>1ρ</SUB> data to be about 40 and 60 kJ/mol for the two types of anions. These relaxation mechanisms have been confirmed by further experiments on a partially deuterated sample.
- 公益社団法人 日本化学会の論文
著者
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Furukawa Yoshihiro
The Institute of Scientific and Industrial Research, Osaka University
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Kiriyama Hideko
The Institute of Scientific and Industrial Research, Osaka University
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