===== On Hydrogen Fluoride, HF, in Space =====

The //J// = 2 – 1 transition HF was detected in absorption toward Sgr B2 with the Long Wavelength Spectrometer of the ISO satellite:\\
D. A. Neufeld, J. Zmuidzinas, P. Schilke, and T. G. Phillips,\\
**[[https://doi.org/10.1086/310942|Discovery of Interstellar Hydrogen Fluoride]]**\\
//Astrophys. J.// **488**, L141–L144 (1997).

The //J// = 1 – 0 transition was observed with the HIFI instrument of the //Herschel// satellite toward G10.6-0.4 (W31C) and Orion KL. Absorption dominates in the former case, but also, very surprisingly, in the latter:\\
D. A. Neufeld, P. Sonnentrucker, T. G. Phillips, et al.,\\
**[[https://doi.org/10.1051/0004-6361/201014523|Strong Absorption by Interstellar Hydrogen Fluoride: //Herschel///HIFI Observations of the Sight-Line to G10.6–0.4 (W31C)]]**\\
//Astron. Astrophys.// **518**, Art. No. L108 (2010);\\
T. G. Phillips, E. A. Bergin, D. C. Lis, et. al.,\\
**[[https://doi.org/10.1051/0004-6361/201014570|//Herschel// Observations of EXtra-Ordinary Sources (HEXOS): Detection of Hydrogen Fluoride in Absorption towards Orion KL]]**\\
//Astron. Astrophys.// **518**, Art. No. L109 (2010).

The same transition was also detected in the circumstellar envelope of the carbon rich star CW Leo by:\\
M. Agúndez, J. Cernicharo, L. B. F. M. Waters, L. Decin, P. Encrenaz, D. Neufeld, D. Teyssier, and F. Daniel,\\
**[[https://doi.org/10.1051/0004-6361/201117578|HIFI detection of Hydrogen Fluoride in the Carbon Star Envelope IRC +10216]]**\\
//Astron. Astrophys.// **533**, Art. No. L6 (2011).

More recently this transition has even been detected in emission in the photon-dominated region by:\\
F. F. S. van der Tak, V. Ossenkopf, Z. Nagy, A. Faure, M. Röllig, and E. A. Bergin,\\
**[[https://doi.org/10.1051/0004-6361/201118308|Detection of HF Emission from the Orion Bar]]**\\
//Astron. Astrophys.// **537**, Art. No. L10 (2012).

The //R//(0) rovibrational transition of HF at 4000.989 cm<sup>–1</sup> or 2.499385 μm was detected with CRIRES at the Very Large Telescope in absorption toward V1074 Sco, aka HD 154368, and Elias 29 by:\\
N. Indriolo, D. A. Neufeld, A. Seifahrt, and M. J. Richter,\\
**[[https://doi.org/10.1088/0004-637X/764/2/188|Direct Determination of the HF/H<sub>2</sub> Abundance Ratio in Interstellar Gas]]**\\
//Astrophys. J.// **764**, Art. No. 188 (2013).\\
//R//(0) as well as //R//(1) were also detected toward AFGL 2136 IRS 1.


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Contributor(s): H. S. P. Müller; 03, 2007; 12, 2010; 08, 2011; 07, 2012; 11, 2013

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