Muonium Chemistry—A Review

The muonium atom can properly be regarded as an ultralight isotope of hydrogen, in which the proton nucleus is replaced by a positive muon of only one-ninth its mass. Within the Born-Oppenheimer approximation, the chemical identical up to differences in reaction dynamics; thus, muonium chemistry studies greatly extend the range of observable mass-sensitive effects in chemical kinetics. The theoretical background of muonium chemistry is presented and applied to thermal kinetic studies in both gas- and liquid-phase systems, drawing on current experimental results (primarily from TRIUMF and SIN) which reveal both normal and inverse dynamic isotope effects. Associated phenomena such as muonium hot atom reactions are also discussed.