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Hiby, Julius W. (1939). "Massenspektrographische Untersuchungen an Wasserstoff- und Heliumkanalstrahlen (H3+, H2-, HeH+, HeD+, He-)". Annalen der Physik. 426 (5): 473–487. doi:10.1002/andp.19394260506. First 1986? --Stone (talk) 18:07, 21 June 2008 (UTC)Reply[reply]

Even earlier: Coulson, C. A.; Duncanson, W. E. (1938). "Comparison of Wave-Functions for HeH++ and HeH+". Proc. Roy. Soc. A. 165: 90. doi:10.1098/rspa.1938.0047.((cite journal)): CS1 maint: multiple names: authors list (link). Apparently "first studied by Wolfgang Ketterle in 1986" refers to the first spectroscopic studies of the neutral helium hydride. I found these two papers by Ketterle: W. Ketterle, H. Figger, and H. Walther (1985). "Emission spectra of bound helium hydride". Phys. Rev. Lett. 55: 2941–2944. doi:10.1103/PhysRevLett.55.2941.((cite journal)): CS1 maint: multiple names: authors list (link); W Ketterle, A Dodhy, H Walther (1986). "Bound—free emission of the helium hydride molecule". Chemical Physics Letters. 129 (1): 76–78. doi:10.1016/0009-2614(86)80172-5.((cite journal)): CS1 maint: multiple names: authors list (link). --Itub (talk) 15:47, 23 June 2008 (UTC)Reply[reply]

After a quick literature search, I'm left with the impression that helium hydride ion and helium hydride molecular ion are used much more often than hydrohelium ion. (Actually, the most common is HeH⁺, but I'd rather use words.) Should we rename the article?

Just thinking aloud, "hydride" suggests a H^- in there, which seems a bit strange. Is that what people really call it? --Rifleman 82 (talk) 09:47, 24 June 2008 (UTC)Reply[reply]

That's exactly what I thought, but people do call it that way. I suppose the rationale is that the neutral molecule, HeH, is reasonably called helium hydride (unless you want to call it hydrogen heliide?), so this cation is the molecular ion (in the mass spectrometry sense) of helium hydride. --Itub (talk) 09:55, 24 June 2008 (UTC)Reply[reply]

The rename sounds like a good idea. Use the most common term that's not an abbreviation. Graeme Bartlett (talk) 22:00, 24 June 2008 (UTC)Reply[reply]

The current image is misleading - HHe⁺ is isoelectronic with H₂, and therefore the two atoms in the cation should have identical size. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:12, 28 December 2011 (UTC)Reply[reply]

I doubt they are the same size. With a higher charge on the nucleus the He+ would be smaller. Graeme Bartlett (talk) 08:06, 3 May 2012 (UTC)Reply[reply]

Then the image is still wrong, because it shows the He⁺ (cyan) larger than the H (silvery grey). Double sharp (talk) 15:00, 30 May 2012 (UTC)Reply[reply]

According to MO theory, the positive charge is distributed over the whole anion, not localised to one atom. Plasmic Physics (talk) 19:53, 30 May 2012 (UTC)Reply[reply]

I suppose we need to find a reference that has done a numerical calculation of the distribution of electron probability in this ion. Bonds can have a polar nature, and a He+ ion is smaller than a H atom. Graeme Bartlett (talk) 21:37, 30 May 2012 (UTC)Reply[reply]

The article is very keen on not referring to the helium hydride ion as a molecule, which is in line with IUPAC Gold book's definition ("An electrically neutral entity..."). The term compound is also avoided, though I could not find a similar definition, for me compounds are also electrically neutral, and thus I consider helium hydride ion to be a polyatomic ion, not a compound. However, the article is categorized in "helium compounds", and the navbox also describes this ion as a compound, while for neon it says no compounds have been identified yet – although neon also forms heteronuclear polyatomic ions. I believe this should be clarified and a uniform terminology be used. In my opinion these are not compounds, but I would be very much interested in others view. Szaszicska (talk) 17:39, 28 June 2013 (UTC)Reply[reply]

Fixed. Plasmic Physics (talk) 21:53, 28 June 2013 (UTC)Reply[reply]

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What will be the pK_a values of HNe⁺ and HAr⁺ Anoop Manakkalath (talk) 08:27, 29 November 2018 (UTC)Reply[reply]

Binding energy for argonium HAr⁺ is 369 kJ mol⁻¹ (quite a bit higher), and I don't know this info for neonium HNe⁺. I cannot find any publications on pKa either. Graeme Bartlett (talk) 10:40, 29 November 2018 (UTC)Reply[reply]

The article has the following computation of the pH:

The hypothetical aqueous acidity can be estimated using Hess's law:

HeH+(g)	→	H+(g)	+ He(g)	+178 kJ/mol	[2]
HeH+(aq)	→	HeH+(g)		+973 kJ/mol	(a)
H+(g)	→	H+(aq)		−1530 kJ/mol
He(g)	→	He(aq)		+19 kJ/mol	(b)
HeH+(aq)	→	H+(aq)	+ He(aq)	−360 kJ/mol

(a) Estimated to be same as for Li⁺(aq) → Li⁺(g).

(b) Estimated from solubility data.

A free energy change of dissociation of −360 kJ/mol is equivalent to a pK_a of −63.

There are no sources for this computation, and it contains two rather dubious estimations, including one (a) that is more than twice the magnitude of the final result. It seems to be original speculation. If there is no reliable source, should it be removed? --Jorge Stolfi (talk) 12:49, 21 April 2019 (UTC)Reply[reply]

In addition, acidities or basicities should be computed using free energy values throughout, not enthalpy ones. Patrizio 93.150.82.18 (talk) 20:02, 10 April 2023 (UTC)Reply[reply]

The article says The helium hydride ion is formed during the decay of tritium in the molecule HT or tritium molecule T2. What about the deuterium-tritium molecule DT (²H−³H)? I suppose that it yields ²H−³He⁺ too, right? --Jorge Stolfi (talk) 20:02, 21 April 2019 (UTC)Reply[reply]

It would, so if you can find a reference you can add it! Perhaps someone has done the experiment. Graeme Bartlett (talk) 23:17, 21 April 2019 (UTC)Reply[reply]

Comparing with dihydrogen cation [H₂]⁺ and trihydrogen cation [H₃]⁺, shouldn't this be helium hydrogen cation or helium hydrogen ion?

And consider the ion [D₂H]⁺ isotopologue of [H₃]⁺ (actually used for something: ^[1]). Should that be "hydrogen deuterium deuteride ion", "dideuterium hydride ion", "hydrogen dideuteride ion", "deuterium hydrogendeuteride ion", "deuterium deteriumhydride ion" -- or just "dideuterium hydrogen ion"? --Jorge Stolfi (talk) 00:48, 23 April 2019 (UTC)Reply[reply]

Well "Helium-hydrogen cation" gets one use in history, helium hydrogen cation has never been used according to Google Scholar. Helium-hydrogen ion gets a few uses, but helium hydrogen ion does not appear to be used like that. Helium-hydride ion also gets a little bit of use as does helium hydride molecular ion. Helium-hydride-ion is used once. Helium hydride ion is in more than 100 papers and appears the most common after HeH+. My favourite, hydrogen helide is also a possible name, but also hardly used. Graeme Bartlett (talk) 10:36, 23 April 2019 (UTC)Reply[reply]

None of your names for [D₂H]⁺ appear to have been used according to Google. Graeme Bartlett (talk) 10:41, 23 April 2019 (UTC)]Reply[reply]

Thnks for searching, and for clarifying that it is more like He⁻−H⁺ than the other way around. My point was that the use of salt nomenclature is problematic for H+2 and H+3 when the atoms are different isotopes. Does IUPAC nomenclature take polarity into account, so that "hydrogen helide" should be the right IUPAC name? If so, shouldn't CO be officially named "oxygen carbide"? 😊
As for "helium hydrogen molecular ion", I don't read the "molecular" as part of the name, but only as a somewhat pleonastic qualifier thrown in for that particular instance. Like one could say "the helium hydrogen heteronuclear ion" or "the helium hydrogen stable ion".
And as for "helium hydride" being most common, presumably that use (like "carbon monoxide") started before the true polarity was established, and people just assumed that the H would be the negative side? Or people just didn't care, or thought that "helium hydride" would raise fewer referee eyebrows than "hydrogen helide"? --Jorge Stolfi (talk) 12:08, 23 April 2019 (UTC)Reply[reply]

Since HeH+ is a powerful acid, shouldn't it be named using acid names, specifically binary acid names (Hydro- -ic), so Hydrohelic acid? 98.45.220.183 (talk) 04:23, 1 February 2022 (UTC)Reply[reply]

According to Alan Guth's book "The Inflationary Universe", around 1/3 of Lithium was produced in the Big Bang. So H / He was'nt the only early chemistry players, as this article seems to indicate. — Preceding unsigned comment added by BenSWiki (talk • contribs) 02:25, 24 April 2019 (UTC)Reply[reply]

• It has the claim to being the oldest heteroatomic molecule. (Lithium vapor is monoatomic.) The press apparently missed the "heteroatomic" part. The dihydrogen cation and trihydrogen cation may be just as old. --Jorge Stolfi (talk) 08:57, 24 April 2019 (UTC)Reply[reply]

How can HeH⁺ be "isoelectronic" with H₂ if it has one fewer electrons? —DIV (137.111.13.48 (talk) 02:36, 24 April 2019 (UTC))Reply[reply]

• [HeH]⁺ has two electrons. The neutral molecule HeH (for as long as it exists) has three.--Jorge Stolfi (talk) 06:50, 24 April 2019 (UTC)Reply[reply]

The article claims that HeH(+) was the first compound to exist in our universe. Well, yes and no; mostly no. If I can use an analogy, there was this 'pea soup' of H, He, and Li and all sorts of combinations of them. This soup was too hot for any of the molecular ions or molecules to exist for more than a "split-second". If we think of the expansion of the Universe (near Recombination (a handful of million to several dozen million years after the Big Bang, z >100)) as draining this pea soup, cooling and reducing its density, then the first island to emerge from the soup was likely HeH(+). That doesn't mean the other species aren't there, it just means they're still 'under' the soup and so not visible. Likewise, the first neutral element was He, and of course the first neutral molecule was H2. The *real* reason I looked into this (see Lepp et al., 2002) is because I doubted that they claimed HeH(+) is a compound. It is not, imho. They don't use the term, compound, at all. A compound must be electrically neutral. Good luck finding that as part of any definition! But if someone can point to an authoritative source which either states ions (without counter ions) are chemical compounds OR said source gives an ion (unbalanced electrically) as an example of a chemical compound, then at least the editors will be justified to make such a (incorrect) claim.98.21.212.117 (talk) 00:19, 23 May 2023 (UTC)Reply[reply]