===== Reports on the Detection of Oxydanium, H3O+, in the ISM ===== Two groups reported almost simultaneously the detection of the //J_K^v_t// = 1₁^– – 2₁⁺ at 307192.41 MHz:\\ J. M. Hollis, E. B. Churchwell, E. Herbst, and F. C. de Lucia,\\ **[[https://doi.org/10.1038/322524a0|An Interstellar Line Coincident with the P(2,1) Transition of Hydronium (H₃O⁺)]]**\\ //Nature// **322**, 524–626 (1986);\\ with the NRAO 12 m telescope toward Orion KL; and\\ A. Wootten, F. Boulanger, M. Bogey, F. Combes, P. J. Encrenaz, M. Gerin, and L. Ziurys,\\ **[[https://ui.adsabs.harvard.edu/abs/1986A%26A...166L..15W|A Search for Interstellar H₃O⁺]]**\\ //Astron. Astrophys.// **166**, L15–L18 (1986); with the NRAO 12 m telescope toward OMC-1 (essentially identical to Orion KL) and Sgr B2(OH).\\ **Note:** see below for the Orion KL case !\\ \\ Later, additional transitions have been reported, e.g. the 3₂⁺ – 2₂^– transition at 364797.427 MHz:\\ A. Wootten, J. G. Mangum, B. E. Turner, M. Bogey, F. Boulanger, F. Combes, P. J. Encrenaz, and M. Gerin,\\ **[[https://doi.org/10.1086/186178|Detection of Interstellar H₃O⁺ – A Confirming Line]]**\\ //Astrophys. J.// **380**, L79–L83 (1991),\\ toward OMC-1, Sgr B2(OH) and (N).\\ \\ The 3₀⁺ – 2₀^– transition at 396272.412 MHz along with the previously mentioned transitions have been detected in several hot core sources:\\ T. G. Phlips, E. F. van Dishoek, J. Keene,\\ **[[https://doi.org/10.1086/171945|Interstellar H₃O⁺ and its Relation to the O₂ and H₂O Abundances]]**\\ //Astrophys. J.// **399**, 533–550 (1992).\\ The sources, in which the cation reportedly was detected newly, are W3 IRS5 (aka W3 M), W3(OH), W51 M, and G34.3 +0.15.\\ \\ A line detected at 4.3121 (5) THz with KOA was tentativel assigned to the 4₃^– – 3₃⁺ transition:\\ R. Timmermann, T. Nikola, A. Poglitsch, N. Geis, G. J. Stacey, and C. H. Townes,\\ **[[https://doi.org/10.1086/310055|Possible Discovery of the 70 Micron H₃O⁺ 4₃^– – 3₃⁺ Transition in Orion BN–IRc2]]**\\ //Astrophys. J.// **463**, L109–L112 (1996);\\ three additional transitions were reported, one of which was overlapped with a line of H₂¹⁸O:\\ J. R. Goicoechea and J. Cernicharo,\\ **[[https://doi.org/10.1086/321712|Far-Infrared Detection of H₃O⁺ in Sagittarius B2]]**,\\ //Astrophys. J.// **554**, L213–L216 (2001).\\ \\ Recent //Herschel///HIFI observations failed to detect any H₃O⁺ in Orion KL near 984.7, 1655.8, and 1657.25 GHz. Thus, previous reports on observations of this molecular ion in Orion KL could no be confirmed. It is possible that emission lines observed at lower frequencies (near 307.2, 364.8, and 396.3 GHz; see above) are caused by other species:\\ H. Gupta, P. Rimmer, J. C. Pearson, et al.,\\ **[[https://doi.org/10.1051/0004-6361/201015117|Detection of OH⁺ and H₂O⁺ towards Orion KL]]**\\ //Astron. Astrophys.// **521**, (2010) Art. No. L47.\\ \\ D. C. Lis, P. Schilke, E. A. Bergin, M. Emprechtinger, and the HEXOS Team\\ reported on\\ **[[https://doi.org/10.1098/rsta.2012.0025|Hot, Metastable Hydronium ion in the Galactic Centre: Formation Pumping in X-Ray-Irradiated Gas?]]**\\ //Phil. Trans. R. Soc. A// **370**, (2012) 5162.\\ Pure inversion transitions of H₃O⁺ with //J// = //K// up to 11 were detected with the HIFI instrument onboard the //Herschel// satellite toward Sagittarius B2(N). Two components were invoked to occur in the envelope of Sgr B2(N), one with a rotational temperature of about 160 K and one with about 520 K.\\ \\ Hot, metastable hydronium was also observed toward Sgr B2(M) and toward W31C outside the Galactic center by\\ D. C. Lis, P. Schilke, E. A. Bergin, M. Gerin, J. H. Black, C. Comito, M. De Luca, B. Godard, R. Higgins, F. Le Petit, J. C. Pearson, E. W. Pellegrini, T. G. Phillips, and S. Yu\\ **[[https://doi.org/10.1088/0004-637X/785/2/135|Widespread Rotationally Hot Hydronium Ion in the Galactic Interstellar Medium]]**\\ //Astrophys. J.// **785**, (2014) Art. No. 135.\\ Values of //T//_rot were (re) determined as 177 ± 54 K and 546 ± 80 K for Sgr B2(M), 172 ± 51 K and 424 ± 48 K for Sgr B2(N), and about 62 K and 360 K for W31C; fewer transitions were detected for this last source and only up to //J// = //K// = 9.\\ \\ ---- Contributor(s): H. S. P. Müller; 01, 2008; 05, 2011; 02, 2026 ----