J. Graham, R. Hannon
Feb 1, 1976
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Influential Citations
18
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Journal
Journal of Chemical Physics
Abstract
Proton magnetic resonance spectra of three crystalline choline halides have been obtained over a temperature range of 77 to 440 °K. In all of these materials the line shapes are strong functions of temperature with multiple changes observed for each substance. Above 353 °K, the temperature at which a crystal–crystal phase transition occurs, the second moment of 0.9 G2 for choline chloride reflects the presence of isotropic reorientation of the choline ions in the solid. This is just the temperature at which the extremely high radiation sensitivity ceases, suggesting that the existence of this dynamic behavior renders the crystal incapable of supporting the decomposition reaction observed below this temperature. Similar behavior is also observed in choline bromide at a higher temperature. From the temperature dependence of the correlation frequency, activation energies for the motional processes were determined and found to be in the range of 3–4 kcal/mole at low temperature and 12–15 kcal/mole for the hig...