Two groups reported almost simultaneously the detection of the
at 307192.41 MHz:
J. M. Hollis, E. B. Churchwell, E. Herbst, and F. C. de Lucia,
An Interstellar Line Coincident with the P(2,1) Transition of Hydronium (H3O+)
Nature 322, 524626 (1986);
with the NRAO 12 m telescope towards Orion KL; and
A. Wootten, F. Boulanger, M. Bogey, F. Combes, P. J. Encrenaz, M. Gerin, and L. Ziurys,
A Search for Interstellar H3O+
Astron. Astrophys. 166, L15L18 (1986); with the NRAO 12 m telescope towards 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
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,
Detection of Interstellar H3O+ A Confirming Line
Astrophys. J. 380, L79L83 (1991),
towards 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,
Interstellar H3O+ and its Relation to the O2 and H2O Abundances
Astrophys. J. 399, 533550 (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
R. Timmermann, T. Nikola, A. Poglitsch, N. Geis, G. J. Stacey, and C. H. Townes,
Possible Discovery of the 70 Micron H3O+ 43 33+ Transition in Orion BNIRc2
Astrophys. J. 463, L109L112 (1996);
three additional transitions were reported, one of which was overlapped with a line of H218O:
J. R. Goicoechea and J. Cernicharo,
Far-Infrared Detection of H3O+ in Sagittarius B2,
Astrophys. J. 554, L213L216 (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.,
Detection of OH+ and H2O+ towards Orion KL
Astron. Astrophys. 521, (2010) Art. No. L47.