Inversion and inversion-rotation spectrum of 14NH3 in the ν2 excited state

Using the vibration-inversion-rotation Hamiltonian for ammonia [V. Spirko, J. M. R. Stone, and D. Papousek, J. Mol. Spectrosc. 60, 159–178 (1976)], a modified theory is worked out for the Δk = ±3n interactions between the inversion-rotation energy levels of NH3 which takes into account the large amplitude inversion motion. Eighty frequencies of inversion and inversion-rotation transitions and two perturbation-allowed transitions in the ν2 state of 14NH3 are measured in the far-infrared region around 1 THz (≈33 cm−1), mostly with the microwave accuracy, by the radiofrequency spectrometer with acoustic detector. By a least-squares fit of these data and the data of the infrared-microwave two-photon and infrared heterodyne measurements of the ν2 band, a set of molecular constants for the ν2 state of 14NH3 is obtained which reproduces the submillimeterwave data with the accuracy of the experiment.