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Species of µ+ States
“Diamagnetic” µ+ precesses at ωµ/2π [MHz] = 135.5•B [T] e.g. “free” µ+, Mu- = µ+e-e-, molecular ions (N2µ+), compounds (MuHO)
Muonium (Mu = µ+e-): singlet state looks depolarized; triplet state precesses at ωMu ≈ 103•ωµ split by HF interaction. In solids, Mu may be vacuum-like [spherical, with AHF ≈ 4463 MHz], shallow [AHF tiny!] or in between [usually with lattice symmetry imposed on e- wavefunction].
Radical (e.g. C6H6Mu•): complicated frequency spectrum due to “sharing” e- with entire molecule; multiple HF interactions will effectively depolarize the spin system unless a strong external magnetic field is applied.
Notes:
In metals, the ubiquitous diamagnetic state consists of a positive muon screened by conduction electrons.
In insulators & semiconductors there is a rich variety of muonium states, most of which have the symmetry of the lattice imposed on the electronic wavefunction; in truly “shallow” states the electron is almost entirely “out in the lattice” and will have the same effective mass etc. as free electrons in the conduction band.
In gases and liquids, both diamagnetic and muonium states are observed but there are also paramagnetic molecules incorporating the muon and its “extra” (unpaired) electron; such radicals have many interesting properties of their own.