We report on the detection of a narrow feature at 262816.73 MHz towards Orion and the cold prestellar core B1-bS, that we attribute to the 1 0 -0 0 line of the deuterated Ammonium ion, NH 3 D + . The observations were performed with the IRAM 30m radio telescope. The carrier has to be a light molecular species as it is the only feature detected over 3.6 GHz of bandwidth. The hyperfine structure is not resolved indicating a very low value for the electric quadrupolar coupling constant of Nitrogen which is expected for NH 3 D + as the electric field over the N nucleus is practically zero. Moreover, the feature is right at the predicted frequency for the 1 0 -0 0 transition of the Ammonium ion, 262817±6 MHz (3σ), using rotational constants derived from new infrared data obtained in our laboratory in Madrid. The estimated column density is (1.1±0.2)×10 12 cm −2 . Assuming a deuterium enhancement similar to that of NH 2 D, we derive N(NH + 4 )≃ 2.6×10 13 cm −2 , i.e., an abundance for Ammonium of a few 10 −11 .

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The protonated argon ion, 36 ArH + , was recently identified in the Crab Nebula from Herschel spectra. Given the atmospheric opacity at the frequency of its J = 1-0 and J = 2-1 rotational transitions (617.5 and 1234.6 GHz, respectively), and the current lack of appropriate space observatories after the recent end of the Herschel mission, future studies on this molecule will rely on mid-infrared observations. We report on accurate wavenumber measurements of 36 ArH + and 38 ArH + rotation-vibration transitions in the v = 1-0 band in the range 4.1-3.7 μm (2450-2715 cm −1 ). The wavenumbers of the R(0) transitions of the v = 1-0 band are 2612.50135 ± 0.00033 and 2610.70177 ± 0.00042 cm −1 (±3σ ) for 36 ArH + and 38 ArH + , respectively. The calculated opacity for a gas thermalized at a temperature of 100 K and with a linewidth of 1 km s −1 of the R(0) line is 1.6 × 10 −15 × N ( 36 ArH + ). For column densities of 36 ArH + larger than 1 × 10 13 cm −2 , significant absorption by the R(0) line can be expected against bright mid-IR sources.

The recent discovery of ArH + in the interstellar medium has awakened the interest in the chemistry of this ion. In this work, the ion-molecule kinetics of cold plasmas of Ar/H 2 is investigated in glow discharges spanning the whole range of [H 2