ABSTRACT
The muon mass is 1/9th the mass of a proton, or 1/18th the mass of a deuteron. Muonium, in a chemical sense, is a light isotope of atomic hydrogen and shows the same chemical behaviour, except when dynamics leads to isotope effects. The unprecedented mass ratio makes the muon and the Mu atom particularly sensitive probes of quantum phenomena. Particles which are confined in a potential well have a zero-point energy which disappears in the classical limit of infinite mass, but it is very significant for muons and for Mu atoms confined in regions of space of atomic dimensions. Transverse field muon spin rotation observes a muon nuclear magnetic resonance transition, which in multi-spin paramagnetic systems is equivalent to an electron-nuclear double resonance transition. Avoided level crossing resonances can be observed for diamagnetic systems with quadrupolar coupling terms, but mostly they have been studied for paramagnetic systems in solids, liquids, and gases.
