The derivation of the rotational potential function from atom–atom potentials. V. Hindered rotation of ammonia molecules in solid ammonia

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Abstract
The rotational potential functions of ND3 and NH3 are calculated from atom–atom potentials. The site symmetry of the ammonia molecules in solid ammonia is C3. The hindered rotational energy levels of the molecules in ND3 and NH3 are computed by diagonalizing the Hamiltonian matrices. The librational frequencies and the activation energy of the ammonia molecules determined from the hindered rotational energy levels are compared to the observed results. The heat capacities of both NH3 and ND3 have been analyzed using the computed hindred rotational energy levels. The difference in the low temperature heat capacities of ND3 and NH3 is interpreted in terms of the hindered rotational energy levels of the molecules.