Hindered rotational energy levels of a tetrahedron in a tetragonal crystalline field

The hindered rotational energy levels of a tetrahedron in a tetragonal crystalline field have been computed. The symmetry group of the Hamiltonian is T̄×D2, where T̄ is the tetrahedral group of rotations about body-fixed axes and D2 represents the tetragonal group of rotations about space-fixed axes. The parameters in the potential function are determined for the tetragonal phases of NH4Br and NH4I assuming an electrostatic model.