The transition state model proposed for muonium formation in solids is critically discussed with respect to the delayed capture model. The two models differ mainly in how the electron capture at the muon is treated. In the delayed capture model the electron stems from the ionization track of the implanted muon. Important electron mobility information is derived in several papers from the time the electron needs to arrive at the muon. In our transition state model, the electron is picked up in the charge-exchange regime during slowing down and is present already when the muon stops in the target. Thus, no information about electron mobility can be obtained from such measurements.

• Received 17 January 2020
• Accepted 7 February 2020

DOI:https://doi.org/10.1103/PhysRevB.101.077202