Kinetic energies of exotic H atoms at formation and cascade

The complex balance of processes occurring at the cascade of exotic H-atoms is usually described by the so-called standard cascade model, but this mod el neglects variations of the kinetic energy T of the exotic atom during th e cascade which are crucial for the analysis of several important experimen ts. New experimental results on T-mu p at H-2 pressures between 0.063 and 4 hPa demonstrate the importance of acceleration due to Coulomb de-excitatio n processes at highly excited mu p levels n>9. The data at the lowest densi ty are sensitive to the initial values of the kinetic energy and n-levels a t the moment of atomic capture. From the measured low-energy tail of the T- mu p-distribution it can be concluded that a considerable part of the mu p( 2s) atoms is metastable at pressures of a few hPa.