The effect of deuteration on the motion of ammonium ions and the structural phase transition in NH4AuCl4

The effect of deuteration on the motion of ammonium ions and/or the structu ral phase transition in NH4AuCl4 was studied by means of Cl-35 nuclear quad rupole resonance measurements. The transition temperature shifted by 5 K fr om 28.5 K for NH4AuCl4 to 33.5 K for ND4AuCl4. Spin-lattice relaxation caus ed by the modulation of the electric field gradient due to the motion of ne arby ammonium ions was observed. The activation energy of the motion of the ammonium ions was determined to be 0.8 and 1.8 kJ mol(-1) for NH4AuCl4 and ND4AuCl4, respectively. By the use of the simple harmonic oscillator model , the barrier height V-0 and the number of wells n of the potential for the reorientation of the ammonium ions were determined as V-0 = 4.2 kJ mol(-1) and n = 4 from the above activation energies for the NH4+ and ND4+ reorien tations.