Theory of radiative corrections to Auger and fluorescence yields and dielectronic satellite line intensities

Abstract

The excitation and decay of autoionizing states of multiply charged ions in plasmas can play an important role in the determination of both the distribution of the various charge states and the spectrum of the emitted radiation. All previous theoretical treatments for low-density plasmas are based on the conventional expressions for the Auger and fluorescence branching ratios, in which the autoionization and radiative decay rates are assumed to be additive. Using a two-level atom model, Armstrong, Theodosiou, and Wall and also Haan and Cooper have investigated the effects of the interaction between the final continuum states which result from the autoionization and radiative decay modes. They have shown that this interaction produces an interference which can alter the relative probabilities for decay into the two alternative continuum channels. In the present investigation, the general properties of angular momentum and spherical tensor operators are employed to extend the theory of this interference to the case in which each of the atomic levels consists of a set of 2J+1 degenerate magnetic sublevels, where J is the total electronic angular momentum. In the case where this interference involves only a single term in the partial-wave expansion for the electron-continuum state, the expressions obtained for the Auger and fluorescence branching ratios are in agreement with those derived in the previous investigations. When several terms in the electron-continuum partial-wave expansion are involved, the Auger and fluorescence branching ratios contain terms corresponding to the interference between different partial-wave components analogous to those which occur in the expression for the photoelectron angular distribution asymmetry parameter. The electromagnetic interaction between the final continuum states of the combined atom plus quantized radiation field system may be expressed in terms of the matrix elements for either the photoelectric transition or the inverse radiative recombination process connecting the final atomic states. Finally, the corrected expressions are obtained for the resonant electron-impact excitation rates and the intensities of the dielectronic satellite lines resulting from the decay of autoionizing states of multiply charged ions in plasmas. The modifications to the conventional expression for the satellite line intensities may be interpreted as terms corresponding to the interference between the direct radiative recombination and dielectronic recombination processes together with radiative corrections to the dielectronic recombination process.