15min:

J. C. PEARSON, S. YU AND B. J. DROUIN, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA; O. PIRALI, M.-A. MARTIN, M. VERVLOET AND D. BALCON, Ligne AILES--Synchrotron SOLEIL, L'Orme des Merisiers Saint-Aubin, 91192 Gif-sur-Yvette, France; C. P. ENDRES, I. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany.

The problem of coupling between a large amplitude motion state and a small amplitude vibration state remains an area of considerable interest and few conclusions in molecular physics. The ₄ and 2 ₂ states of NH₃ provide an excellent opportunity to study the coupling of large and small amplitude motions in an inversion system where the quantum mechanics have been worked out in detail . In spite of the well established Hamiltonian, a large body of high quality spectra remains to fit to experimental accuracy. Several recent studies have resulted in 2-10 times the infrared accuracy over restricted ranges of quantum numbers and have either been unable to fit or have completely ignored the 162 reported microwave transitions . Assessment of the perturbations details provides some insight into why previous analyses might have not completely succeeded; however, the ability of current Hamiltonian to completely model the large amplitude inversion coupled with small amplitude vibration remains to be adequately addressed. We report extensive new measurements of the rotation-inversion transitions in the ₄ and 2 ₂ states, a global analysis of existing data and provide a complete assessment of the inversion-rotation-vibration Hamiltonian in NH₃.