Effect of external electric fields on the dielectronic recombination cross section of lithium and sodium like ions

Abstract

The effect of external electric fields on the dielectronic recombination cross section associated with the 2s ..-->.. 2p excitation in the Li like ions B/sup 2 +/, C/sup 3 +/, O/sup 5 +/, and Fe/sup 23 +/, and the 3s ..-->.. 3p excitation in the Na like ions Mg/sup +/, S/sup 5 +/, Cl/sup 6 +/, and Fe/sup 15 +/ has been studied in the configuration-average, distorted-wave approximation. By applying the linear-Stark approximation to the doubly-excited 2pnl and 3pnl Rydberg states in the presence of an external electric field, we study the systematics of field mixing effects on dielectronic recombination and determine the maximum field enhancement of the dielectronic recombination cross section. We find that the magnitude of the field enhancement decreases as we move up an isoelectronic sequence and is of the order of a factor of two or three in highly-ionized systems. In addition, we show that dielectronic recombination transitions through doubly-excited states near threshold can produce large narrow peaks in the cross section at low energies, which are especially prominent in high stages of ionization, and are not affected by the electric field.