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>Proton spinndash;lattice relaxation studies of molecular motion and phase transitions in solid choline chloride, bromide, iodide, and perchlorate
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Proton spinndash;lattice relaxation studies of molecular motion and phase transitions in solid choline chloride, bromide, iodide, and perchlorate
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机译：Proton spinndash;lattice relaxation studies of molecular motion and phase transitions in solid choline chloride, bromide, iodide, and perchlorate
Proton spinndash;lattice relaxation time measurements in both the Zeeman and rotating frames (T1andT1rgr;) are reported for the choline ion, Me3+NCH2ndash;CH2OH, in four of its polycrystalline salts, the chloride, bromide, iodide, and perchlorate. In each system, the following motional processes are identified as being responsible for spinndash;lattice relaxation: (i) rotation of the methyl groups at low temperatures, followed successively by (ii) the onset of motion of+NMe3moiety about the long chain Cndash;N (denoted as Cprime;3) axis, (iii) general reorientation of the whole choline cation, and (iv) additional slow motion of the long chain CH2CH2OH in the case of the chloride and bromide, and (v) diffusion of the choline ion in the case of the iodide and perchlorate. From a quantitative analysis of the data, activation energies for the above types of motion are determined. A crystalndash;crystal phase transition which is known to occur at 353, 364, and 362thinsp;thinsp;K in the chloride, bromide, and iodide, respectively, is found to occur at a much lower temperature (272thinsp;thinsp;K) in the perchlorate lattice. Evidence is also presented for a new high temperature phase transition at 430thinsp;thinsp;K in the iodide, at which point a rsquo;rsquo;quenchingrsquo;rsquo; of the diffusional process is found in this structure.
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