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.