QUANTUM-MECHANICS OF THE ROTATION-TRANSLATION COUPLING OF NH3-GROUPS IN METAL HEXAAMMINE SALTS

The family of metal hexaammine salts Me(NH3)(6)Y-2 with Me = Ni,Co is characterized by a wealth of different distributions of the protons of the disordered NH3 group. We find a transition from nearly unhindered rotation with Y = PF6 to weak localization on the four corners of a s quare with Y = I. This is based on a gradually increasing rotation-tra nslation coupling of the motion. Low-temperature measurements do not a llow an interpretation of these phenomena in terms of Boltzmann densit ies. We ha ie therefore calculated the proton density on the basis of a complete quantum mechanical Hamiltonian which takes into account the rotation-translation coupling caused by a fourth-order anharmonic cry stal potential. The quantum mechanical model removes all the difficult ies we encountered earlier with Boltzmann densities.