Abstract
The authors report on the motion of oxygen atoms in some ammonium salts as studied by the measurement of the spin-lattice relaxation time T1 rho , of protons in the rotating frame. The temperature dependence of T1 rho for protons shows extremely large minimum values (T1 rho )min=1-3 sin NH4ClO4, (NH4)2-Cr2O7, (NH4)2S2O8 and (NH4)2Ce(NO3)6 at relatively high temperatures ( approximately=300K). T1 rho has also been measured for protons in partially deuterated ammonium perchlorate and ammonium dichromate. It is found that values of (T1 rho )min are independent of the concentration of the deuterons. The large minimum values, 1-3 s, or T1 rho are attributed to the reorientations of the anions that modulate the dipolar interaction between the protons in ammonium ions and the natural abundance of 17O(0.037%) in the anions. The activation energies for the reorientations of the anions ClO4, CrO3, NO3 and SO3 were also determined.
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