The J = 1 – 0 transition was observed in emission with the SPIRE instrument of the Herschel satellite toward the ultra-luminous infrared galaxie (ULIRG) Mrk 231:
P. P. van der Werf, K. G. Isaak, R. Meijerink, et al.,
Black Hole Accretion and Star-Formation as Drivers of Gas Excitation and Chemistry in Markarian 231
Astron. Astrophys. 518, (2010) Art. No. L42.
The account is sparse, but a detail of the spectrum (van der Werf, private communication) clearly shows the line well-separated from a near-by water line.

The same transition was seen with the same instrument in absorption toward the ULIRG Arp 220 by
N. Rangwala, P. R. Maloney, J. Glenn, et al.,
Observations of Arp 220 Using //Herschel//-SPIRE: An Unprecedented View of the Molecular Gas in an Extreme Star Formation Environment
Astrophys. J. 743, (2011) Art. No. 94.

R. R. Monje, T. G. Phillips, R. Peng, D. C. Lis, D. A. Neufeld, and M. Emprechtinger
reported on the
Discovery of Hydrogen Fluoride in the Cloverleaf Quasar at //z// = 2.56
Astrophys. J. 743, (2011) Art. No. 94;
employing the CSO. Again, the J = 1 – 0 transition was observed in absorption.

Contributor(s): H. S. P. Müller; 12, 2010; 04, 2013