Low-energy characteristics of photoionization cross section for Fe25+ ion embedded in hot dense plasma

Complex multi-body interactions between ions and surrounding charged particles exist in hot and dense plasmas, and they can screen the Coulomb potential between the nucleus and electrons and significantly change the atomic structures and dynamic properties, thereby further affecting macroscopic plasma properties such as radiation opacity and the equation of state. Using the atomic-state-dependent (ASD) screening model, we investigate the photoionization dynamics of Fe25+ ions in hot and dense plasma. The photoionization cross section for all transition channels and total cross sections of n ≤ 2 states for Fe25+ ions are studied in detail, and the low-energy characteristics induced by plasma screening are also investigated. Compared with the classical Debye Hückel model, the ASD model introduces degeneracy effects through inelastic collision processes, resulting in higher plasma density requirements for bound electrons to merge into the continuum. Near the threshold, the photoionization cross section obeys the Wigner threshold law after considering the screening effect. As the energy increases, the cross sections show low-energy characteristics such as shape resonance, Cooper minimum, low-energy enhancement, and Combet-Farnoux minimum, which can significantly increase or reduce the cross section of the corresponding energy region. For example, the low-energy enhancement in the 2p→εs1/2 channel increases the cross section by several orders of magnitude, drastically changing the properties of the photoelectron spectrum. It is significant to study the low-energy characteristics for understanding the physical properties of the photoionization cross section. Fe is an important element in astrophysics. The cross section results in the medium and high energy regions calculated by the ASD model in this work can provide theoretical and data support for investigating hot and dense plasmas in astrophysics and laboratory.