The simple diatomic NH⁺ radical cation (imidogen cation) was the subject of an unsuccessful search reported in 2014 by Persson and co-workers that followed previous unsuccessful searches reported in 2010 and 2012. These three studies focused on the Sgr B2(M) and W31C star-forming regions. Parallel work by Benz and co-workers from 2013 was also unable to detect NH⁺ in two other star-forming regions, AFGL 2591 and W3 IRS5. The analyses from all four publications utilized data collected by the Herschel Space Observatory that functioned from 2009 to 2013. The rotational transitions of NH⁺ sought in these studies fall in the terahertz region.

NH⁺ can be formed by ionizing the imidogen radical, NH, which was first detected in the ISM in 1991. NH⁺ is also known as the aminyliumyl cation, which is something of a mouthful.