Abstract
Investigations of inelastic neutron scattering in cubic ammonium hexachlorides that have almost identical structures give the following energies E1 for the first excited NH4+ torsional state at 82K: 7.5 meV for (NH4)2PdCl6, 8 meV for (NH4)2PtCl6, 14.5 meV for (NH4)2SnCl6, 15.5 meV for (NH4)2PbCl6 and 18 meV for (NH4)2TeCl6. The relation between E1 and activation energies Ea for NH4+ reorientation from proton relaxation differs from that of most other ammonium salts. The shape of the potential seen by NH4+ is discussed Ea and E1 are found to be very sensitive functions of the structure parameters.