Helium dimer
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| Names | |
|---|---|
| Other names
dihelium | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| 48 | |
PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |
| He2 | |
| Molar mass | 8.005204 g·mol−1 |
| Appearance | colorless gas |
| Thermochemistry | |
Std enthalpy of formation (ΔfH⦵298) |
-1.1×10−5 kcal/mol |
| Related compounds | |
Related van der Waals molecules |
LiHe NeHe2 He3 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references | |
A helium dimer is a molecule composed of two helium atoms. One type of helium dimer is a van der Waals molecule with formula He2 consisting of two helium atoms. This chemical is the largest diatomic molecule—a molecule consisting of two atoms bonded together. The bond that holds this dimer together is so weak that it will break if the molecule rotates or vibrates too much. It can only exist at very low cryogenic temperatures.
Another type of helium dimer is two excited helium atoms bonded to each other. This form is called an excimer, and was discovered from a spectrum of helium that contained bands first seen in 1912. Written as He2* with the * meaning an excited state, it is the first known Rydberg molecule.
Several dihelium ions also exist, having net charges of negative one, positive one, and positive two. Also two helium atoms can be confined together without bonding in the cage of a fullerene.