DIPOLE MOMENT AND ROVIBRATIONAL INTENSITIES IN THE ELECTRONIC GROUND STATE OF NH$_3$: BRIDGING THE GAP BETWEEN AB INITIO THEORY AND SPECTROSCOPIC EXPERIMENT

{S. N. Yurchenko, M. Carvajal, P. Jensen, H. Lin, J. Zheng, and W. Thiel, \textit{Mol. Phys.Author Institution: Max-Planck-Institut f{u}r Kohlenforschung,; Kaiser-Wilhelm-Platz 1, D--45470 M{u}lheim an der Ruhr, Germany; Departamento de Fisica Aplicada,; Facultad de Ciencias Experimentales, Avda. de las FF.AA. s/n,; Universidad de Huelva, 21071, Huelva, Spain; Department of Chemistry, University of Minnesota,; 207 Pleasant St. SE. Minneapolis, Minnesota 55455; FB C -- Theoretische Chemie,; Bergische Universit{a}t, D--42097 Wuppertal, GermanyWe report theoretical values for the transition moments of an extensive set of vibrational bands in the electronic ground state of $^{14}$NH$_3$. For selected bands, we have further made detailed simulations of the rotational structure. The calculations are carried out by means of recently developed computational procedures for describing the nuclear motion% } \textbf{103}, 359-378 (2005) and references therein.} and are based on a high-level {\it ab initio} potential energy surface, and high-level dipole moment surfaces, for the electronic ground state of NH$_3$. The reported theoretical intensity values are compared to, and found to agree very well with, corresponding experimental results. It is believed that the computational method, in conjunction with high-quality {\it ab initio} potential energy and dipole moment surfaces, can simulate rotation-vibration spectra of XY$_3$ pyramidal molecules prior to observation with sufficient accuracy to facilitate the observation of t hese spectra. By degrading the accuracy of selected elements of the calculations, we have also investigated the influence of customary approximations on the computed intensity values