[1] While using an early form of mass spectrometry to study the resultant species of plasma discharges, he discovered a large abundance of a polyatomic ion with a mass-to-charge ratio of 3.

Since the signal grew stronger in pure hydrogen gas, he correctly assigned the species as H+3.

[3] This led to the suggestion of Watson and Herbst & Klemperer in 1973 that H+3 is responsible for the formation of many observed molecular ions.

[4][5] It was not until 1980 that the first spectrum of H+3 was discovered by Takeshi Oka,[6] which was of the ν2 fundamental band (see #Spectroscopy) using a technique called frequency modulation detection.

Emission lines were detected in the late 1980s and early 1990s in the ionospheres of Jupiter, Saturn, and Uranus.

[7][8][9] In the textbook by Bunker and Jensen[10] Figure 1.1 reproduces part of the ν2 emission band from a region of auroral activity in the upper atmosphere of Jupiter, [11] and its Table 12.3 lists the transition wavenumbers of the lines in the band observed by Oka[6] with their assignments.

[12] In 1998, H+3 was unexpectedly detected by McCall et al. in a diffuse interstellar cloud in the sightline Cygnus OB2#12.

[13] In 2006 Oka announced that H+3 was ubiquitous in interstellar medium, and that the Central Molecular Zone contained a million times the concentration of ISM generally.

[14] The three hydrogen atoms in the molecule form an equilateral triangle, with a bond length of 0.90 Å on each side.

[18] The concentration of H+2 is what limits the rate of this reaction in nature - the only known natural source of it is via ionization of H2 by a cosmic ray in interstellar space: The cosmic ray has so much energy, it is almost unaffected by the relatively small energy transferred to the hydrogen when ionizing an H2 molecule.

The dominant destruction pathway in dense interstellar clouds is by proton transfer with a neutral collision partner.

Its strong dipole and high abundance make it easily detectable by radioastronomy.

The major product is dissociation into three hydrogen atoms, which occurs roughly 75% of the time.

The most abundant molecule in dense interstellar clouds is 1H2 which also has ortho and para states, with total nuclear spins 1 and 0, respectively.

Also, with a broadband source like the Sun, there is plenty of radiation to pump the H+3 to higher energy states from which it can relax by spontaneous emission.

[22] Unexpectedly, three H+3 lines were detected in 1998 by McCall et al. in the diffuse interstellar cloud sightline of Cyg OB2 No.

Since then, H+3 has been detected in many other diffuse cloud sightlines, such as GCS 3–2,[21] GC IRS 3,[21] and ζ Persei.