Ammonium ion diffusion in the superprotonic phase of (NH 4) 3H(SO 4) 2 as studied by 1H spin-lattice relaxation times in the rotating frame

Abstract

Ammonium ion diffusion in (NH 4) 3H(SO 4) 2 has been studied by means of 1H spin-lattice relaxation times in the rotating frame, T 1 ρ . The 1H T 1 ρ values were measured at 200.13 MHz in the ranges of 380 to 490 K. The ammonium protons and the acidic protons have independent T 1 ρ values, suggesting that the spin diffusion between the two species is ineffective. The translational diffusion of the ammonium ions is the most dominant mechanism to relax both the ammonium protons and the acidic protons in phase I. The 1H T 1 ρ values in phase I are analyzed theoretically and the motional parameters are obtained. The activation energy ( E a) is 75 kJ mol − 1 and the mean residence time at the infinite temperature ( τ 0) is 4.0 × 10 − 15 s. This motion is three or four orders of magnitude slower than that of the acidic protons.