Enhanced Dielectronic Recombination in Crossed Electric and Magnetic Fields

Abstract

Photorecombination is the inverse of photoionization and is the process by which a free electron simultaneously emits a photon and makes a transition to a bound state. It is the purpose of this paper to show that certain types of photorecombination processes can be greatly enhanced in static, crossed electric and magnetic fields. Besides being intrinsically interesting, this enhancement may affect the interpretation of recent experiments on photorecombination in static electric fields and affect the recombination rate in some tenuous astrophysical plasmas. Burgess and Summers [1] suggested that under some circumstances the dielectronic recombination (DR) rate could be enhanced due to angular momentum redistribution during three-body collisions. DR is photorecombination that proceeds through the capture of an electron by an ion in an autoionizing state; the incident electron induces a transition in the ion but loses so much energy it is captured into a resonance state. Before the electron can regain the energy from the core electrons and leave the ion, a photon is emitted and the electron is captured into a bound state. Jacobs et al. [2,3] showed that , redistribution of the autoionizing state due to plasma (electric) microfields can strongly enhance the DR rate. The prototypical example for studying field effects is the DR of a Li-like ion. The initial state is a free electron, and the ion is in the 1s 2 2s configuration. The autoionizing state is 1s 2 2pn,. The system is stabilized by the 2p electron emitting a photon, leaving the system in the 1s 2 2sn, bound state. The physical reason for enhanced DR in a static field can be understood in a time dependent picture. The electron is initially captured in an n, state while simultaneously exciting the core. If an electric field is on, the Rydberg state will precess into states of higher angular momentum. Since the autoionization rate rapidly decreases with angular momentum, this has the effect of making photon emission more probable. In the more traditional time independent picture, the