The chemistry of ammonia (NH_3) in the circumstellar envelopes (CSEs) of AGB stars and red supergiants is poorly understood. Thermodynamic equilibrium (TE) chemistry predicts an abundance of < 10~(-8)), orders of magnitudes below values reported from observations (?10~(-7)-10~(-6)). To date, there is no consistent model explaining the origin of such high abundances. To better understand the physical conditions necessary for the formation of NH_3,we analysed the NH_3 rotational and inversion lines observed in the spectrum of IK Tauri. The strength of the rotational lines clearly confirms the high abundances as compared to the TE predictions. From 1D radiative transfer modelling including infrared pumping via vibrational bands, we infer a total NH_3 abundance of 7.5 x 10~(-7), along with an ortho-to-para ratio (OPR) of < 1.5: 1,slightly above the statistical equilibrium value of 1. We discuss these preliminary results and the possible origin of NH_3 in oxygen-rich CSEs.
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