R-matrix calculations for opacities: III. Plasma broadening of autoionizing resonances

TL;DR

This paper investigates how plasma conditions like electron collisions, Stark effects, and thermal Doppler broadening influence autoionizing resonances in iron ions, affecting their photoionization cross sections and resonance profiles.

Contribution

It provides a comprehensive formulation and quantitative analysis of plasma broadening effects on autoionizing resonances using R-matrix data for multiple iron ion states.

Findings

Significant broadening and shifting of AI resonances due to plasma effects.

Resonance strengths are redistributed but their integrated values are preserved.

Resonance complexes become broadened and eventually dissolve into continua.

Abstract

A general formulation is employed to study and quantitatively ascertain the effect of plasma broadening of {\it intrinsic} autoionizing (AI) resonances in photoionization cross sections. In particular, R-matrix data for iron ions described in the previous paper in the RMOP series (RMOP-II, hereafter RMOP2) are used to demonstrate underlying physical mechanisms due to electron collisions, ion microfields (Stark), thermal Doppler effects, core excitations, and free-free transitions. Breit-Pauli R-matrix (BPRM) cross section for the large number of bound levels of Fe ions are considered, 454 levels of Fe~XVII, 1,184 levels of Fe~XVIII and 508 levels of Fe~XIX. Following a description of theoretical and computational methods, a sample of results is presented to show significant broadening and shifting of AI resonances due to {\it Extrinsic} plasma broadening as a function of temperature and density. Redistribution of AI resonance strengths broadly preserves their integrated strengths as well as the naturally {\it intrinsic} asymmetric shapes of resonance complexes which are broadened, smeared and flattened, eventually dissolving into the bound-free continua.