Rearrangement in antihydrogen–atom scattering

I discuss rearrangement in low-energy collisions between atoms (ions) and antihydrogen. For many atoms there exists a critical internuclear distance below which the leptons are no longer bound to the heavy particles. At this critical distance the Born–Oppenheimer approximation breaks down. I briefly discuss the case of general atoms. Numerical examples are given for the simple proton–antihydrogen system, which has the advantage that the Born–Oppenheimer approximation can be solved exactly. I study the convergence of the optical potential approach for this system.