Seventy-nine microwave transitions of the v4 = 1 and v2 = 2 s states of 14NH3, including two forbidden rotational transitions with the selection rules Δk = ±1, Δl = ⊣2, have been measured up to 400 GHz. The ν4 and 2ν2 s band spectra of the molecule have also been recorded by a Fourier-transform infrared spectrometer with a resolution of 0.005 cm-1 and an accuracy of 0.0002 cm-1. More than 700 infrared transitions have been assigned up to the J = 14 rotational levels. The obtained microwave and infrared data were fitted to a 91-parameter Hamiltonian in which several Δ(k - l) = ±3 interaction terms were explicitly considered together with existing microwave results. The determined molecular constants for the v4 = 1 and v2 = 2s states reproduce the observed data with a root mean square deviation of 0.00038 cm-1.
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