Spin-Lattice Relaxation of Proton in Ammonium Perchlorate: Effect of the Motion of Oxygen Atoms

Abstract

Spin-lattice relaxation times T_1ρ of protons (¹H) in the rotating frame were determined in ammonium perchlorate NH₄ClO₄ between 556 K and 125 K. The temperature dependence of T_1ρ shows two minimum values 1.5 sec at about 476 K and 0.94 sec at 238 K for an rf field H₁=2.1 gauss. The origins of the minima T_1ρ are attributed to the motion of oxygen atoms ¹⁷O of natural abundance (0.037%). Oxygen atoms affect T_1ρ of protons in different two ways. The minimum of T_1ρ at higher temperature is due to the cross relaxation between ¹H and ¹⁷O spins, while that at low temperature due the the reorientation of ClO₃-ions which modulates the dipolar interaction between ¹H and ¹⁷O and also due to the cross relaxation between ¹H and ¹⁷O. The value e²qQ⁄h=12.3 MHz was determined for ¹⁷O in ClO₄-ion.