Calculated cross sections for the electron-impact ionization of Na(ns) and Na(nd) Rydberg atoms

Recent experiments (Nagesha and MacAdam 2003 Phys. Rev. Lett. 91 113202) determined electron-impact ionization cross sections for 11 selected Na(ns) and Na(nd) Rydberg states (with the principal quantum number n in the range of 35–51), which exceeded predictions based on the well-known Vriens–Smeets (VS) fitting formula by more than an order of magnitude. This motivated us to extend the semi-classical Deutsch–Mark (DM) formalism to the calculation of ionization cross sections of these Na Rydberg states. The results show that the calculated DM ionization cross sections also lie below the experimentally determined cross sections by factors ranging from 15 to about 40. This indicates either that the ionization of these Rydberg atoms involves some new aspects or mechanisms that are not adequately described by models based on low-n data, or that the very difficult experiments suffered from a systematic error in the absolute calibration process that remained unrecognized.