Investigation of the H1 Spin-Lattice Relaxation Times of Some Ammonium Compounds

The temperature dependence of the proton spin-lattice relaxation times of (NH4)2A1(S04)2, (NH4)2 M0O4, NH4NH2S03 and (NH4)2SnCl6 has been investigated in the temperature range 100— 500 K. The experimental results indicate that intra H-H dipolar interaction, modulated by reorientational motion of the ammonium ion, is the dominant relaxation mechanism between 100 and 200 K. The activation energies for the reorientational motion of the ammonium ions were found to be 1.54, 1.56, 0.99, and 0.91 kcal/mole, respectively. Furthermore, it has been detected that above 200 K the spin-rotational interactions of the ammonium ions contribute to the spin-lattice relaxation. The average value of the mean-square spinrotational interaction constant for NH4+ was found to be C2 = 1.42 x 101 0s-2 .