Trihydrogen cation

Trihydrogen cation
Names
	IUPAC name Hydrogenonium
Identifiers
CAS Number	28132-48-1 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:30479;
ChemSpider	21865043;
Gmelin Reference	249
CompTox Dashboard (EPA)	DTXSID801315416 ;
	InChI InChI=1S/H3/c1-2-3-1/q+1 Key: RQZCXKHVAUFVMF-UHFFFAOYSA-N;
	SMILES [H+]1[H][H]1;
Properties
Chemical formula	H+3
Molar mass	3.024 g·mol−1
Conjugate base	Dihydrogen, H2
Related compounds
Other anions	Hydride
Other cations	Hydrogen ion; Dihydrogen cation; Hydrogen ion cluster;
Related compounds	Trihydrogen
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The trihydrogen cation or protonated molecular hydrogen (IUPAC name: hydrogenonium ion) is a cation (positive ion) with formula H+3, consisting of three hydrogen nuclei (protons) sharing two electrons.

The trihydrogen cation is one of the most abundant ions in the universe. It is stable in the interstellar medium (ISM) due to the low temperature and low density of interstellar space. The role that H+3 plays in the gas-phase chemistry of the ISM is unparalleled by any other molecular ion.

The trihydrogen cation is the simplest triatomic molecule, because its two electrons are the only valence electrons in the system. It is also the simplest example of a three-center two-electron bond system.