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- Shmuel Albert
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801
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- John A. Ripmeester
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801
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説明
<jats:p>Crystalline dimethylacetylene (CH3–C≡C–CH3) was investigated by broad line and pulsed proton magnetic resonance in the temperature interval 217–77°K. The NMR second moment and line shape at 77°K along with the fact that we did not notice a change in the free induction decay following a 90° pulse in our experiments, agree with the presence of only methyl group rotation about the C–C axis in the entire temperature region of investigation. From the temperature dependence of the spin-lattice relaxation time (T1) we find that the CH3 group rotation in the low temperature phase is fast (ω0τc≪ 1) and its activation energy is 830±40 cal/mole. A discontinuity in the T1 curve was observed at the phase transition. In the high temperature phase the CH3 group rotation is enhanced and the possibility of the motion being a free rotation, or nearly so, is considered from the relatively long and temperature independent T1 behavior. We also discuss other possible relaxation mechanisms which could occur in the high temperature phase besides the dipolar one. The phase transition in DMA is discussed in view of available thermodynamic and x-ray as well as our NMR data.</jats:p>
収録刊行物
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- The Journal of Chemical Physics
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The Journal of Chemical Physics 57 (12), 5336-5339, 1972-12-15
AIP Publishing
