Ammonium Ions Dynamics in NH4Br – Proton NMR T1 Measurements and Simulations

The p-T phase diagram [2, 3] for this compound is given in Figure 1. Generally, different models of motion of the ammonium ions are proposed for different phases, and many research papers deal with this problem. Numerous papers [4 10] were devoted to NMR T j relaxation time calculations for different types of anisotropic reorientations of the ammonium cation. An extensive review of ammonium ion studies by different methods can be found in [11]. The dynamics of ammonium ions in NH4C1 was also studied in our laboratory [ 12], in which case a proton Van Vleck [13] second moment was calculated for different models of ammonium ion motion in a single crystal. The main aim of this paper was to get further insight into ammonium cation reorientation in phase II and III at normal pressure. To achieve this, calculations of relaxation times Tx were performed for different models of reorientations. Our calculations of Tx were based on the Monte Carlo simulation of correlation functions with both intraand interionic interactions taken into account. Inclusion of the interTEMPERATURE /K