Recent from talks
Helium dimer
Knowledge base stats:
Talk channels stats:
Members stats:
Helium dimer
The 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.
Two excited helium atoms can also bond to each other in a form called an excimer. This 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. Two helium atoms can be confined together without bonding in the cage of a fullerene.
Based on molecular orbital theory, He2 should not exist, and a chemical bond cannot form between the atoms. However, the van der Waals force exists between helium atoms as shown by the existence of liquid helium, and at a certain range of distances between atoms the attraction exceeds the repulsion. So a molecule composed of two helium atoms bound by the van der Waals force can exist. The existence of this molecule was proposed as early as 1937.
He2 is the largest known molecule of two atoms when in its ground state, due to its extremely long bond length. The He2 molecule has a large separation distance between the atoms of about 5,200 picometres (52 Å). This is the largest for a diatomic molecule without rovibronic excitation. The binding energy is only about 1.3 mK, 10−7 eV or 1.1×10−5 kcal/mol.
Both helium atoms in the dimer can be ionized by a single photon with energy 63.86 eV. The proposed mechanism for this double ionization is that the photon ejects an electron from one atom, and then that electron hits the other helium atom and ionizes that as well. The dimer then explodes as two helium cations repel each other, moving with the same speed but in opposite directions.
A dihelium molecule bound by Van der Waals forces was first proposed by John Clarke Slater in 1928.
The helium dimer can be formed in small amounts when helium gas expands and cools as it passes through a nozzle in a gas beam. Only the isotope 4He can form molecules like this; 4He3He and 3He3He do not exist, as they do not have a stable bound state. The amount of the dimer formed in the gas beam is of the order of one percent.
Hub AI
Helium dimer AI simulator
(@Helium dimer_simulator)
Helium dimer
The 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.
Two excited helium atoms can also bond to each other in a form called an excimer. This 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. Two helium atoms can be confined together without bonding in the cage of a fullerene.
Based on molecular orbital theory, He2 should not exist, and a chemical bond cannot form between the atoms. However, the van der Waals force exists between helium atoms as shown by the existence of liquid helium, and at a certain range of distances between atoms the attraction exceeds the repulsion. So a molecule composed of two helium atoms bound by the van der Waals force can exist. The existence of this molecule was proposed as early as 1937.
He2 is the largest known molecule of two atoms when in its ground state, due to its extremely long bond length. The He2 molecule has a large separation distance between the atoms of about 5,200 picometres (52 Å). This is the largest for a diatomic molecule without rovibronic excitation. The binding energy is only about 1.3 mK, 10−7 eV or 1.1×10−5 kcal/mol.
Both helium atoms in the dimer can be ionized by a single photon with energy 63.86 eV. The proposed mechanism for this double ionization is that the photon ejects an electron from one atom, and then that electron hits the other helium atom and ionizes that as well. The dimer then explodes as two helium cations repel each other, moving with the same speed but in opposite directions.
A dihelium molecule bound by Van der Waals forces was first proposed by John Clarke Slater in 1928.
The helium dimer can be formed in small amounts when helium gas expands and cools as it passes through a nozzle in a gas beam. Only the isotope 4He can form molecules like this; 4He3He and 3He3He do not exist, as they do not have a stable bound state. The amount of the dimer formed in the gas beam is of the order of one percent.
Recent media