Collisions of Na⁺ions with Na Rydberg atoms in electric fields: depopulation cross sections and final-state distributions from 36s and 30p initial states

An experimental study of the depopulation and final-state distribution of Na 36s and 30p Rydberg states under Na + bombardment in the presence of electric fields up to 50 V cm -1 has been carried out. Incident energies E from 171 to 967 eV span the range from 0.6 to. 1.4 times the mean orbital speed of the excited electron in the initial state. Absolute depopulation cross sections of order 10 -8 cm 2 , believed accurate within 25%, are reported as functions of field and energy. sigma 36s is proportional to E -1 , but sigma 30p is nearly independent of energy. The distribution of final states was measured by selective field ionization. At weak fields for which the initial state is well separated from the nearest Stark manifold, final states are broadly distributed across the nearest manifolds. But for stronger fields that shift the initial state close to a Stark manifold the final states are strongly concentrated among the energetically closest manifold sublevels.