In 2012, De Luca and coworkers reported the detection of HCl⁺, the radical cation formed when hydrogen chloride is ionized. The observations were performed with the HIFI instrument on the Herschel orbital observatory. HCl⁺ was detected toward two star-forming regions, W31C (G10.6-0.4) and W49N. The radical character gives rise to doublet features—closely spaced pairs of lines—which are helpful for detecting such species. The laboratory rotational spectrum of HCl⁺ was measured by Gupta et al. and published back-to-back in ApJL with the interstellar detection. No confirming observations have evidently been perfomed to date.

Related species: HCl was detected in 1985, and protonated HCl (H₂Cl⁺) was detected in 2010.