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We report theoretical values for the transition moments of an extensive set of vibrational bands in the electronic ground state of $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$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.