Hydrogen chloride (HCl) was identified in 1985 by
Blake et al. in
Orion Molecular Cloud 1 as observed with the
Kuiper Airborne Observatory
(the predecessor of SOFIA). Although only one rotational
transition was observed,
hyperfine splitting due to
interaction of electrons with the Cl nucleus results in three closely spaced lines. HCl was later detected in
Sgr B2 via the same feature by Zmuidzinas et al.
in 1995 and subsequently in Orion A and
Monoceros R2 by
Salez et al. in 1996 and in
IRC +10216 and
W3 A in two studies by Cernicharo and co-workers
published in 2010 based upon observations with the
Herschel Space Observatory.
The detection of HCl via its rotational spectrum was confirmed in 1995 by observation of one its
electronic transitions in ζ Oph by
Federman et al. with the
Hubble Space Telescope.
HCl is well known in terrestrial
chemistry. In water, it is a strong acid,
which can be used, for example, to
etch or decoratively stain concrete.
Yet HCl is also extensively used in the pharmaceutical industry
to make water soluble forms of drugs.