A proton magnetic resonance study of the motion of NH+4 in dilute solid solutions of NH4Cl in RbCl and KCl

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Abstract
The temperature dependence of the proton spin–lattice relaxation times of dilute solid solutions of about 3 mol % NH4Cl in RbCl and KCl are studied in the range 5–300 K. The potential barriers hindering the NH+4 reorientations are found to be extremely small (∼150 cal/mol). The relaxation rates are found to depart significantly from the usual semiclassical values: at 6 K the semiclassical relaxation rates are some 40 times greater than experimental ones. This departure from the semiclassical theory is partly explained by including the effects of symmetry and the quantization of the molecular rotational states.