Motion of Methylammonium Ions in Solid CH3NH3NO3 and CH3NH3SCN Studied by 1H NMR

The proton spin-lattice relaxation time T1 at 20 MHz and the second moment of 1H NMR absorptions at 40 MHz were determined at various temperatures between 77 and 300 K for CH3NH3NO3 and CH3NH3SCN, and their partially deuterated analogs, CH3ND3NO3 and CH3ND3SCN. A phase transition was located at 242 K for CH3NH3SCN. The fully protonated compounds yielded two T1 minima, the low- and high-temperature one of which could be attributed to the reorientation of the CH3 and NH3+ groups, respectively, of the cation about the C–N bond axis. The activation energy was evaluated for these motional modes.