Influence of the Naturally Abundant ¹⁷O on the Spin-Lattice Relaxation Time T_1ρ of Protons in Ammonium Sulfate

Abstract

Proton spin-lattice relaxation times T₁ and T_1ρ in partially deuterated ammonium sulfate were measured between 357 K and 118 K. The minimum values of T_1ρ (2∼4 sec) in the paraelectric phase were attributed to the random modulation of the dipolar interaction between the protons in NHD₃⁺ and the natural abundance of the ¹⁷O (0.037%) in SO₄⁻². The activation energy E_a∼4.1 kcal/mol for the reorientation of SO₄⁻² was determined.