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Molecular helium

Molecular helium is a form (allotrope) of the chemical element helium that contains chemical bonds. Helium is a noble gas and normally exists as a single atom, written just He, but it can form molecules in special conditions.

Dimeric He2

Two helium atoms can make a molecule that is bound by the van der Waals force. This He2 molecule is only stable at extremely low temperatures.

He2 is the largest known diatomic molecule (molecule made of two atoms), with a distance between the helium atoms of 52 ångströms.[1]

He2* excimer

A different type of He2 exists when the helium atoms are in an excited state. A molecule that is more stable in an excited state than the ground state is called an excimer, and is written with a * symbol. He2* was the first excimer discovered by scientists. [2]

Trimeric He3

Trimeric helium is made of three atoms. Like dimeric helium, it is bound by the van der Waals force. The He3 trimer is larger but more stable than He2.[3]

Sources

  1. ↑ Grisenti, R. E.; Schöllkopf, W.; Toennies, J. P.; Hegerfeldt, G. C.; Köhler, T.; Stoll, M. (2000). "Determination of the Bond Length and Binding Energy of the Helium Dimer by Diffraction from a Transmission Grating". Physical Review Letters. 85 (11): 2284–2287. Bibcode:2000PhRvL..85.2284G. doi:10.1103/PhysRevLett.85.2284. PMID 10977992.
  2. ↑ Epée Epée, M. D.; Motapon, O.; Chakrabarti, K.; Tennyson, Jonathan (2024). "Theoretical investigation of Rydberg states of He 2 using the R-matrix method". Molecular Physics. 122 (15–16). Bibcode:2024MolPh.12295013E. doi:10.1080/00268976.2023.2295013.
  3. ↑ Voigtsberger, J.; Zeller, S.; Becht, J.; Neumann, N.; Sturm, F.; Kim, H.-K.; Waitz, M.; Trinter, F.; Kunitski, M.; Kalinin, A.; Wu, J.; Schöllkopf, W.; Bressanini, D.; Czasch, A.; Williams, J. B.; Ullmann-Pfleger, K.; Schmidt, L. Ph H.; Schöffler, M. S.; Grisenti, R. E.; Jahnke, T.; Dörner, R. (2014). "Imaging the structure of the trimer systems 4He3 and 3He4He2". Nature Communications. 5. doi:10.1038/ncomms6765. PMID 25488049.



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