November 2011

Hydrogen chloride

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.


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