===== Detection of HCO+ in the ISM =====
D. Buhl and L. E. Snyder\\
detected an\\
**[[https://doi.org/10.1038/228267a0|Unidentified Interstellar Microwave Line]]**\\
//Nature// **228**, 267–269 (1970)\\
strongly in emission at 89190 ± 2 MHz toward the high-mass star-forming regions W3(OH), Orion, Sgr A NH3A) and W51 and toward the dark cloud L134 using the 11 m NRAO telescope.
W. Klemperer\\
concomitantly suggested the\\
**[[https://doi.org/10.1038/2271230a0|Carrier of the Interstellar 89.190 GHz Line]]**\\
//Nature// **227**, 1230 (1970)\\
to be the ground state transition of HCO+ based on structure considerations.
R. C. Woods, T. A. Dixon, R. J. Saykally, and P. G. Szanto\\
proved this suggestion by measuring the\\
**[[https://doi.org/10.1103/PhysRevLett.35.1269|Laboratory Microwave Spectrum of HCO+]]**\\
//Phys. Rev. Lett.// **35**, 1269–1272 (1975)\\
at the frequency derived from radio astronomical observations.
L. E. Snyder, J. M. Hollis, F. J. Lovas, and B. L. Ulich\\
reported slightly later on the\\
**[[https://ui.adsabs.harvard.edu/abs/1976ApJ...209...67S|Detection, Identification, and Observations of Interstellar H13CO+]]**\\
//Astrophys. J.// **209**, 67–74 (1976)\\
at 86754 MHz, close to the predicted frequencies. The NRAO 11 m telecope was used, and the line was detected in several sources: DR21, DR21(OH), NGC 2264, NGC 7538, Rrion A, Sgr B2(OH), W3(OH), W49, W51, and W75N.
The **[[https://ui.adsabs.harvard.edu/abs/1976ApJ...209L..83H|Radio Detection of Interstellar DCO+]]**\\
//Astrophys. J.// **209**, L83–L85 (1976)\\
with the NRAO 11 m telecope toward DR21(OH), L134, and NGC 2264 was reported by\\
J. M. Hollis, L. E. Snyder, F. J. Lovas, and D. Buhl.
M. Guélin and P. Thaddeus\\
reported on the\\
**[[https://ui.adsabs.harvard.edu/abs/1976ApJ...209L..83H|Detection of HC18O+ in Sagittarius B2]]**\\
//Astrophys. J.// **209**, L139–L141 (1979)\\
again using the NRAO 11 m telecope.
M. Guélin, W. D. Langer, and R. W. Wilson\\
studied the distribution of 5 isotoplogs of HCO+ in several sources:\\
**[[https://ui.adsabs.harvard.edu/abs/1982A%26A...107..107G|The State of Ionization in Dense Molecular Clouds]]**\\
//Astron. Astrophys.// **107**, 107–127 (1982).\\
The observations were performed with the Bell Lab. 7 m telescope. In the course of the investigations, D13CO+ was detected in TMC-1 and in L183.
M. Guélin, J. Cernicharo, and R. A. Linke\\
described the\\
**[[https://ui.adsabs.harvard.edu/abs/1982ApJ...263L..89G|Detection of HC17O+ in Sagittarius&nsp;B2]]**\\
//Astrophys. J.// **263**, L89–L93 (1982)\\
using the Bell Lab. 7 m telescope.
HCO+ was also detected in the diffuse medium toward the extragalactic contiunuum sources QSO B0212+735, $C 50.11 (NRAO150), and BL Lac by\\
R. Lucas and H. Liszt,\\
**[[https://ui.adsabs.harvard.edu/abs/1982ApJ...263L..89G|Plateau de Bure Observations of mm-wave Molecular Absorption from 13CO, HCO+, and HCN]]**\\
//Astron. Astrophys.// **282**, L5–L8 (1994).
L. M. Ziurys, E. D. Tenenbaum, R. L. Pulliam, N. J. Woolf, and S. N. Milam,\\
**[[https://doi.org/10.1088/0004-637X/695/2/1604|Carbon Chemistry in the Envelope of VY Canis Majoris: Implications for Oxygen-Rich Evolved Stars]]**\\
//Astrophys. J.// **695**, 1604–1613 (2009);\\
detected HCO+ in the circumstellar envelope of this star using the ARO 12 m dish as well as the ARO SMT.
R. L. Pulliam, J. L. Edwards, and L. M. Ziurys,\\
studied the\\
**[[https://doi.org/10.1088/0004-637X/743/1/36|Circumstellar Ion-Molecule Chemistry: Observations of HCO+ in the Envelopes of O-rich Stars and IRC+10216]]**\\
//Astrophys. J.// **743**, Art. No. 36 (2011).\\
CW Leo, also known as IRC+10216, is a carbon-rich AGB star. Again, the ARO 12 m dish as well as the ARO SMT were employed.
J. R. Najita, J. S. Carr, S. E. Strom, D. M. Watson, I. Pascucci, D. Hollenbach, U. Gorti, and L. Keller\\
reported on\\
**[[https://doi.org/10.1088/0004-637X/712/1/274|//Spitzer// Spectroscopy of the Transition Object TW Hya]]**\\
//Astrophys. J.// **712**, 274–286 (2010).\\
The observation of overlapping //Q//-branch transitions of the ν2 band of HCO+ near 829.2 cm–1 appears to be not only the first observation of this band in a young stellar object, but probably the first infrared observation of HCO+ in space.
N. S. Hakobian and R. M. Crutcher\\
detected the\\
**[[https://doi.org/10.1088/2041-8205/758/1/L18|First Interstellar HCO+ Maser]]**\\
//Astrophys. J.// **712**, 274–286 (2010)\\
through CARMA observations of its 1 – 0 transition in direction of the DR21(OH)-1 methanol maser region.
----
Contributor(s): H. S. P. Müller; 11, 2012
----