Detection of the Ammonium Ion in Space

TL;DR

This paper reports the first detection of the deuterated Ammonium ion NH3D+ in space, using radio telescope observations, and discusses its spectral features, abundance, and implications for astrochemistry.

Contribution

It provides the first observational evidence of NH3D+ in space, confirming its spectral line and estimating its abundance in interstellar environments.

Findings

Detected NH3D+ in Orion and B1-bS.

Estimated column density of 1.1×10^12 cm^-2.

Derived Ammonium abundance of a few 10^-11.

Abstract

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, NH3D+. 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 NH3D+ 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 (3sigma), using rotational constants derived from new infrared data obtained in our laboratory in Madrid. The estimated column density is 1.1(0.2)e12 cm-2. Assuming a deuterium enhancement similar to that of NH2D, we derive N(NH4+) sim 2.6e13 cm-2, i.e., an abundance for Ammonium of a few 1e(-11).