Editing Hydronium (section)

===Astronomical detections===
As early as 1973 and before the first interstellar detection, chemical models of the interstellar medium (the first corresponding to a dense cloud) predicted that hydronium was an abundant molecular ion and that it played an important role in ion-neutral chemistry.<ref name=herbst1973fad>{{cite journal |last1=Herbst |first1=E. |last2=Klemperer |first2=W. |year=1973 |title=The formation and depletion of molecules in dense interstellar clouds |journal=[[The Astrophysical Journal]] |volume=185 |page=505 |doi=10.1086/152436 |bibcode=1973ApJ...185..505H|doi-access=free}}</ref> However, before an astronomical search could be underway there was still the matter of determining hydronium's spectroscopic features in the gas phase, which at this point were unknown. The first studies of these characteristics came in 1977,<ref name=schwarz1977gpi>{{cite journal |last1=Schwarz |first1=H.A. |year=1977 |title=Gas phase infrared spectra of oxonium hydrate ions from 2 to 5&nbsp;μm |journal=[[Journal of Chemical Physics]] |volume=67 |issue=12 |page=5525 |doi=10.1063/1.434748 |bibcode=1977JChPh..67.5525S}}</ref> which was followed by other, higher resolution spectroscopy experiments. Once several lines had been identified in the laboratory, the first interstellar detection of H<sub>3</sub>O<sup>+</sup> was made by two groups almost simultaneously in 1986.<ref name=hollis1986ilc /><ref name=wootten1986sih /> The first, published in June 1986, reported observation of the ''J''{{su|b=''K''|p=vt}}&nbsp;=&nbsp;1{{su|b=1|p=−}}&nbsp;−&nbsp;2{{su|b=1|p=+}} transition at {{val|307192.41|u=MHz}} in [[OMC-1]] and [[Sgr B2]]. The second, published in August, reported observation of the same transition toward the [[Orion-KL]] nebula.

These first detections have been followed by observations of a number of additional {{H3O+}} transitions. The first observations of each subsequent transition detection are given below in chronological order:

In 1991, the 3{{su|b=2|p=+}}&nbsp;−&nbsp;2{{su|b=2|p=−}} transition at {{val|364797.427|u=MHz}} was observed in OMC-1 and Sgr B2.<ref name=wootten1991myx>{{Cite journal |doi=10.1086/186178 |title=Detection of interstellar H<sub>3</sub>O<sup>+</sup> – A confirming line |journal=[[The Astrophysical Journal]] |volume=380 |pages=L79 |year=1991 |last1=Wootten |first1=A. |last2=Turner |first2=B. E. |last3=Mangum |first3=J. G. |last4=Bogey |first4=M. |last5=Boulanger |first5=F. |last6=Combes |first6=F. |last7=Encrenaz |first7=P. J. |last8=Gerin |first8=M. |bibcode=1991ApJ...380L..79W}}</ref> One year later, the 3{{su|b=0|p=+}}&nbsp;−&nbsp;2{{su|b=0|p=−}} transition at {{val|396272.412|u=MHz}} was observed in several regions, the clearest of which was the W3&nbsp;IRS&nbsp;5 cloud.<ref name=phillips1992iha />

The first far-IR 4{{su|b=3|p=−}}&nbsp;−&nbsp;3{{su|b=3|p=+}} transition at 69.524&nbsp;μm (4.3121&nbsp;THz) was made in 1996 near [[Becklin–Neugebauer Object|Orion BN]]-IRc2.<ref name=timmermann1996pdm>{{Cite journal | doi = 10.1086/310055| title = Possible discovery of the 70&nbsp;μm {H<sub>3</sub>O<sup>+</sup>} 4{{su|b=3|p=−}}&nbsp;−&nbsp;3{{su|b=3|p=+}} transition in Orion BN-IRc2| journal = [[The Astrophysical Journal]]| volume = 463| issue = 2| pages = L109| year = 1996| last1 = Timmermann | first1 = R. | last2 = Nikola | first2 = T. | last3 = Poglitsch | first3 = A. | last4 = Geis | first4 = N. | last5 = Stacey | first5 = G. J. | last6 = Townes | first6 = C. H. | bibcode = 1996ApJ...463L.109T| doi-access = free}}</ref> In 2001, three additional transitions of {{H3O+}} in were observed in the far infrared in Sgr&nbsp;B2; 2{{su|b=1|p=−}}&nbsp;−&nbsp;1{{su|b=1|p=+}} transition at 100.577&nbsp;μm (2.98073 THz), 1{{su|b=1|p=−}}&nbsp;−&nbsp;1{{su|b=1|p=+}} at 181.054&nbsp;μm (1.65582 THz) and 2{{su|b=0|p=−}}&nbsp;−&nbsp;1{{su|b=0|p=+}} at 100.869&nbsp;μm (2.9721 THz).<ref name=goicoechea2001fid>{{Cite journal |doi=10.1086/321712 |title=Far-infrared detection of H<sub>3</sub>O<sup>+</sup> in Sagittarius B2 |journal=[[The Astrophysical Journal]] |volume=554 |issue=2 |pages=L213 |year=2001 |last1=Goicoechea |first1=J. R. |last2=Cernicharo |first2=J. |bibcode=2001ApJ...554L.213G|doi-access=free|hdl=10261/192309 |hdl-access=free }}</ref>