Vibration-inversion-rotation spectra of ammonia. A vibration-inversion-rotation Hamiltonian for NH3

A new model Hamiltonian has been developed to study the vibration-inversion-rotation energy levels of ammonia. In this model the inversion motion is removed from the vibrational problem by allowing the molecular reference configuration to be a function of the large amplitude motion coordinate. The treatment follows closely that developed by Hougen, Bunker, and Johns for the study of triatomic molecules.The numerical methods that have been used to solve the zeroth-order Hamiltonian describing the inversion-rotation energy levels of NH₃ and ND₃ in the ground vibrational state are discussed. Certain group-theoretical problems concerning the symmetry classification of the states of ammonia are also discussed.