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The video is about Muonic Heavy Hydrogen or so called ${}^{4.1}H$ is discussed at the end of this list. Yes, that's pronounced "hydrogen four-point-one." See the New Scientist article Atomic disguise makes helium look like hydrogen, and the primary article published in Science Kinetic Isotope Effects for the Reactions of Muonic Helium and Muonium with H2 Fleming, D. G. et al. Science 28 Jan 2011: Vol. 331, Issue 6016, pp. 448-450, DOI: 10.1126/science.1199421

It has Rydberg states with $E_n \sim -(6.8eV)/n^2$ or half that of normal hydrogen, because the reduced mass is half that for an electron bound to a much heavier item. The longer-lived triplet ${}^3S_1$ state has a mean lifetime of about 142ns, and decays by electron positron annihilation into three gamma-ray photons. It is sometimes studied by slowing and stopping positrons in powdered MgO where they capture an electron and tend to remain relatively unperturbed by the other atoms.

Muonic helium is created by substituting a muon for one of the electrons in helium-4. The muon orbits much closer to the nucleus, so muonic helium can therefore be regarded like an isotope of helium whose nucleus consists of two neutrons, two protons and a muon, with a single electron outside. Colloquially, it could be called "helium 4.1", since the mass of the muon is slightly greater than 0.1 amu. Chemically, muonic helium, possessing an unpaired valence electron, can bond with other atoms, and behaves more like a hydrogen atom than an inert helium atom.

Muonic heavy hydrogen atoms with a negative muon may undergo nuclear fusion in the process of muon-catalyzed fusion, after the muon may leave the new atom to induce fusion in another hydrogen molecule. This process continues until the negative muon is trapped by a helium atom, and cannot leave until it decays.

The video is about Muonic Heavy Hydrogen or so-called ${}^{4.1}H$ is discussed at the end of this list. Yes, that's pronounced "hydrogen four-point-one." See the New Scientist article Atomic disguise makes helium look like hydrogen, and the primary article published in Science Kinetic Isotope Effects for the Reactions of Muonic Helium and Muonium with H2 Fleming, D. G. et al. Science 28 Jan 2011: Vol. 331, Issue 6016, pp. 448-450, DOI: 10.1126/science.1199421

It has Rydberg states with $E_n \sim -(6.8eV)/n^2$ or half that of normal hydrogen because the reduced mass is half that for an electron bound to a much heavier item. The longer-lived triplet ${}^3S_1$ state has a mean lifetime of about 142ns, and decays by electron-positron annihilation into three gamma-ray photons. It is sometimes studied by slowing and stopping positrons in powdered MgO where they capture an electron and tend to remain relatively unperturbed by the other atoms.

Muonic helium is created by substituting a muon for one of the electrons in helium-4. The muon orbits much closer to the nucleus, so muonic helium can therefore be regarded as an isotope of helium whose nucleus consists of two neutrons, two protons, and a muon, with a single electron outside. Colloquially, it could be called "helium 4.1", since the mass of the muon is slightly greater than 0.1 amu. Chemically, muonic helium, possessing an unpaired valence electron, can bond with other atoms, and behaves more like a hydrogen atom than an inert helium atom.

Muonic heavy hydrogen atoms with a negative muon may undergo nuclear fusion in the process of muon-catalyzed fusion, after which the muon may leave the new atom to induce fusion in another hydrogen molecule. This process continues until the negative muon is trapped by a helium atom, and cannot leave until it decays.

Muonic helium is created by substituting a muon for one of the electrons in helium-4. The muon orbits much closer to the nucleus, so muonic helium can therefore be regarded like an isotope of helium whose nucleus consists of two neutrons, two protons and a muon, with a single electron outside. Colloquially, it could be called "helium 4.1", since the mass of the muon is slightly greater than 0.1 amu. Chemically, muonic helium, possessing an unpaired valence electron, can bond with other atoms, and behaves more like a hydrogen atom than an inert helium atom.

 

Muonic heavy hydrogen atoms with a negative muon may undergo nuclear fusion in the process of muon-catalyzed fusion, after the muon may leave the new atom to induce fusion in another hydrogen molecule. This process continues until the negative muon is trapped by a helium atom, and cannot leave until it decays.

Muonic helium is created by substituting a muon for one of the electrons in helium-4. The muon orbits much closer to the nucleus, so muonic helium can therefore be regarded like an isotope of helium whose nucleus consists of two neutrons, two protons and a muon, with a single electron outside. Colloquially, it could be called "helium 4.1", since the mass of the muon is slightly greater than 0.1 amu. Chemically, muonic helium, possessing an unpaired valence electron, can bond with other atoms, and behaves more like a hydrogen atom than an inert helium atom.

Muonic heavy hydrogen atoms with a negative muon may undergo nuclear fusion in the process of muon-catalyzed fusion, after the muon may leave the new atom to induce fusion in another hydrogen molecule. This process continues until the negative muon is trapped by a helium atom, and cannot leave until it decays.

Muonium is an exotic atom made up of an antimuon and an electron, which was discovered in 1960 and is given the chemical symbol Mu. During the muon's 2.2 µs lifetime, muonium can enter into compounds such as muonium chloride (MuCl) or sodium muonide (NaMu). Due to the mass difference between the antimuon and the electron, muonium (μ+e−) is more similar to atomic hydrogen (p+e−) than positronium (e+e−). Its Bohr radius and ionization energy are within 0.5% of hydrogen, deuterium, and tritium, and thus it can usefully be considered as an exotic light isotope of hydrogen.

Muonium is an exotic atom made up of an antimuon and an electron, which was discovered in 1960 and is given the chemical symbol Mu. During the muon's 2.2 µs lifetime, muonium can enter into compounds such as muonium chloride (MuCl) or sodium muonide (NaMu). Due to the mass difference between the antimuon and the electron, muonium (μ+e−) is more similar to atomic hydrogen (p+e−) than positronium (e+e−). Its Bohr radius and ionization energy are within 0.5% of hydrogen, deuterium, and tritium, and thus it can usefully be considered as an exotic light isotope of hydrogen.