S. Albert, H. S. Gutowsky
Jun 15, 1973
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Influential Citations
52
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Journal
Journal of Chemical Physics
Abstract
The three phases of solid ammonium hexafluorophosphate (NH4PF6) have been studied by cw and pulsed NMR methods between 298° and 77°K. The proton and fluorine second moments of 1.8 and 1.9 G2, respectively, at 298°K are consistent with rapid, randomized reorientations of NH4+ and PF6‐ ions, while the larger values at 77°K require that there be little or no motional narrowing by reorientations of the PF6− ions even though the narrowing by NH4+ reorientations is still present. For both nuclear species the spin‐lattice relaxation time (T1) studies of the two low‐temperature phases reveal three distinct regions: (1) Between 109° and 110°K their relaxation is exponential with time. (2) Between 105° and 87°K the relaxation is nonexponential, but may be expressed as the sum of two exponential terms. At each temperature the same pair of time constants applies to both nuclear species. (3) At 77°K the relaxation is again exponential, with different T1's for protons and fluorine. The nonexponential behavior in region...