Helium dimer

The helium dimer is a <a href="/facts/Van_der_Waals_molecule/qcmsRbu0">van der Waals molecule</a> with formula He2 consisting of two <a href="/facts/Helium/yRul93TG">helium</a> <a href="/facts/Atom/FoQ4kGN5">atoms</a>. This chemical is the largest <a href="/facts/Diatomic_molecule/hkfKAC7m">diatomic molecule</a>—a molecule consisting of two atoms <a href="/facts/Chemical_bond/ArNUMnIB">bonded</a> together. The bond that holds this <a href="/facts/Dimer_(chemistry)/mU64PnEq">dimer</a> together is so weak that it will break if the molecule rotates, or vibrates too much. It can only exist at very low <a href="/facts/Cryogenic/cw7dHAkp">cryogenic</a> temperatures.
Two <a href="/facts/Excited_state/czcLYNnr">excited</a> helium atoms can also bond to each other in a form called an <a href="/facts/Excimer/u5gfyLUI">excimer</a>. This was discovered from a <a href="/facts/Spectrum/wPUjkpqI">spectrum</a> of helium that contained <a href="/facts/Spectral_bands/hw6CxHIS">bands</a> first seen in 1912. Written as He2* with the * meaning an excited state, it is the first known <a href="/facts/Rydberg_molecule/Y7EsngVY">Rydberg molecule</a>.
Several dihelium <a href="/facts/Ion/3bePpDna">ions</a> also exist, having net charges of negative one, positive one, and positive two. Two helium atoms can be confined together without bonding in the cage of a <a href="/facts/Fullerene/LPdnl8ox">fullerene</a>.

Helium dimer open-in-new

Helium dimer