More than two thousand Stark resonances of the ν4 and 2ν2 band transitions of 14NH3 and 15NH3 were observed at Doppler-limited resolution with a CO laser. Fourier transform infrared spectroscopy on 15NH3 is also carried out. Thirty-six new microwave transitions including seven perturbation-enhanced transitions are observed in the v4 = 1 excited vibrational state of 14NH3 and 15NH3. Accuracies of all available spectroscopic data on the v4 = 1 and the v2 = 2 states are evaluated and analyses of the vibration-rotation spectra are performed. The Coriolis interaction between the closely lying v4 = 1 a (antisymmetric level) and v2 = 2 s (symmetric level) states is explicitly included in the analysis. Smaller Coriolis interactions between the v4 = 1 a and the v2 = 1 s states and between the v2 = 2 s and the v2 = v4 = 1 a states (i.e., (v1, v2, v′3, v′4) = (0 1 00 11)) are also taken into consideration. The accuracy in determination of the principal molecular constants is 10-6. The parameters thus obtained reproduce the frequencies of the vibration-rotation transitions and inversion transitions within the accuracy of 0.0024 cm-1.
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