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,
Discovery of Interstellar Hydrogen Fluoride
Astrophys. J. 488, L141L144 (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.,
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.,
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,
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,
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 cm1
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,
Direct Determination of the HF/H2 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.