Muonic atom deexcitation via formation of metastable molecular states, in light of experimental verification

In a recent experiment performed at PSI, a peak in the time-of-flight distribution of pμ(1s) atoms could be identified with decay of ppμ* molecular ions situated below the 2s threshold, providing 900 eV of kinetic energy to the pμ atom. This finding may be interpreted in terms of the side path model which suggests that metastable muonic molecules may form with high probability in resonant collisions between muonic hydrogen in the 2s state and hydrogen molecules, e.g., pμ(2s) + H₂ → [ppμ*)_νJ^pq - Pee]_νK → [(ppμ*)_ν′J′^p′q′ - pe]⁺ + e^-. The Coulombic decay of the Auger stabilised ppμ* molecular ion then leads to the formation of highly energetic pμ(1s) atoms. In the present paper calculations of resonant formation rates in pure hydrogen are presented and compared to the quenching rate of pμ(2s) atoms measured at low hydrogen density.