Y. C. Jean

Muonium atoms and intraspur processes in water

Since muonium atoms come into existence as a result of stopping energetic positive muons, it has been suggested that intraspur reactions (primarily with thermalized electrons or OH radicals, in water) are responsible for: (i) muonium formation, (ii) direct generation of a fraction of the muons in diamagnetic molecules, and (iii) the ’’missing’’ muon polarization. These postulates are examined in detail by adding scavengers which can preclude intraspur reactions without reacting with muonium. The results show convincingly that intraspur processes are insignificant in (i) and (ii). Furthermore, they could only be important in (iii) if a spin‐exchange process occurred with a frequency which was much greater than the ordinary diffusion‐limited encounter frequency. Rather than this ’’spur model’’, the data obtained are consistent with the ’’hot model’’, whereby hot muonium atoms form beyond the spurs of the muon track.

Spin-conversion of muonium by interaction with paramagnetic ions

Abstract Muonium atoms are found to undergo spin-conversion (triplet-to-singlet) with high probability in encounters with paramagnetic (but not diamagnetic) ions in aqueous solution. The spin-flip or spin-exchange process is compared in magnitude with electron-transfer reactions for eleven transition metal ions.

Reply to ‘‘The time‐scale of intraspur muonium formation’’

The spur model ofmuonium formation in water is further elucidated. The comments by percival5 on the authors experiments reported earlier, are answered. (AIP)

Reaction of muonium with O2 in aqueous solution

Abstract The interaction between Mu and O 2 in water, which could be a spin-conversion process, has a rate constant of (2.4 ± 0.5) × 10 10 M −1 s −1 and is compared with the diffusion-controlled limit and the corresponding gas phase reaction.

Determination of the effective charge on muonium during its reaction in aqueous solution

The rate of reaction of muonium atoms with solutes of either charge is unaffected by the addition of a high concentration of an inert salt, therefore the “effective charge” on the muonium at the point of reaction is essentially zero.

Recent results in muonium solution kinetics

Using Muonium Spin Rotation (MSR) techniques the aqueous solution kinetics of several muonium addition reactions and spin conversion interactions have been studied. The addition reactions show both diffusion and activation-controlled reaction rates with isotope effects between 1 and 3 for diffusion-control and between 7 and 31 for activation-control reactions. Barrier energies are typically ≈15 kJ/mole and ≈30 kJ/mole, respectively, for these processes in water. Spin-conversion interactions involving Ni(aq+2 and Ni(cyclam)+2 complexes showed that spin-conversion of “triplet” Mu by a paramagnetic solute occurs at or near the diffusion-controlled limit while the chemical reaction with the diamagnetic configuration of Ni(cyclam)+2 occured some 100 times slower at kM ⩽ 5×108M−1s−1.