Rotational potential functions of ammonium ions in crystalline fields of various symmetries. I

The potential functions are given for the hindered rotation of ammonium ions, when the site symmetries of the ammonium ions are Oh, Td, D2d, D2h, C3v, C3, S4, C4v, C4h, C2v, C2, Cs, and C1. The procedure is outlined for computing the hindered rotational energy levels of an ammonium ion in crystalline fields of Cs or C1 symmetry. If the barrier to rotation is high, equations are given for the computation of the librational frequencies of ammonium ions in crystalline fields of Oh, Td, D2d, and C3v symmetry.