Rotational tunneling of NH 4 and NH 3 D and dipolar interaction in „ NH 3 . 6 D 0 . 4 ... 2 PtCl

At 10% deuteration ammonium hexachloroplatinate still exhibits the cubic phase Fm3m of the protonated material at all temperatures. Rotational tunneling of the ammonium isomers NH4 1 and NH3D 1 was measured by neutron spectroscopy. At temperatures T>18 K the energies and intensities of the observed tunneling transitions agree with a statistical occurrence of ammonium isomers and a cubic environment. Below T518 K there is no change of the NH4 spectrum while the NH3D transition adopts an unresolved broad intensity distribution before it transforms into a new structured low temperature spectrum. The intermediate spectrum is interpreted as fingerprint of a potential distribution of statistically distributed disordered NH3D ions interacting by long-range dipolar coupling. The low-temperature spectrum finds an explanation as frozen minimum energy configurations of coupled NH3D dipoles. A dipole moment of NH3D of 0.05 D can be derived from the difference of tunnel splittings. © 2002 American Institute of Physics. @DOI: 10.1063/1.1477185#