l-changing depopulation of NasandpRydberg states by ion impact

${\mathrm{Ar}}^{+}$ and ${\mathrm{Na}}^{+}$ ion beams bombarding Na ns and np Rydberg-state targets at impact velocities near the Bohr-orbital velocity of the target atoms (i.e., ṽ≊1) induce transitions to (n-1)l states (l≥2) with larger-than-geometric cross sections. Depopulation of ns states proceeds directly into the full n-1, l≥2 manifold rather than populating the np or (n-1)p states as the first of a sequence of dipole-allowed steps. Depopulation of np states leads to a distribution of final states that is dominated by the nearer or high-l part of the n-1 manifold. n dependences of the cross section for ns depopulation are given at several energies for n=32–41 and at a single energy for np, n=26–32. The absolute cross section for Na(36s) depopulation falls gradually but steadily for reduced velocities ṽ increasing from 0.3 to 1.35. Bombardment of Na 39s and 39p states in applied fields 0–18.5 V/cm reveals that the final-state distributions become narrower as manifold states are Stark shifted close to the initial states. No theoretical results are available for direct comparison with these experiments, but the method of coupled channels seems to be the most suitable candidate.