Relativistic Dielectronic Recombination Theory

Abstract

Dielectronic recombination (DR) is an inverse Auger process in which a free electron is captured by a recombining ion to form a doubly excited autoionizing state. The subsequent decay of the autoionizing state to a stabilized bound state by emitting photons completes the recombination process.1–3 DR is an important recombination process for high temperature plasmas. It can affect the ionization balance and level kinetics of the hot plasmas. In addition, the dielectronic satellite lines observed in the emission spectra are frequently used as plasmas diagnostic tools. In the past decade, intense theoretical4–16 and experimental17–24 studies on the DR process have been carried out. Most of the earlier theoretical calculations on the DR rate coefficients were done either by using a term average approximation or in LS coupling without including the effects of relativity and configuration interaction. The early experimental investigations17,18 were concentrated on few times ionized low-Z ions. Recently, the development of electron beam ion trap (EBIT)25, electron beam ion source (EBIS)26 and heavy ion storage ring27 has become possible to produce very highly-charged heavy ions (e.g. U 82+ and Xe53+)24,28 and to study the interaction between electrons and these ions. For highly-charged heavy ions, one expects that the nonrelativistic method would be inadequate and a relativistic treatment is necessary. To meet this challenge we have developed a relativistic package29 based on the multiconfiguration Dirac-Fock method (MCDF)30,31 and have carried out systematic relativistic calculations of DR cross sections and rate coefficientsl4–16 and resonant transfer and excitation cross sections in ion-atom collisions.32,33 In this paper, we will briefly discuss the relativistic calculations of atomic structure and transition rates and will focus our attention on the effects of relativity and intermediate coupling on the DR cross sections and rate coefficients.