Abstract
Statistical models combined with the local plasma frequency approach applied to the atomic electron density are employed to study the photoionization cross-section for complex atoms. It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations, where quantum mechanical approaches that include electron correlations are exceedingly difficult. Quantum mechanical photoionization calculations are studied with respect to energy and nl quantum number for hydrogen-like and non-hydrogen-like atoms and ions. A generalized scaled photoionization model (GSPM) based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl. Explicit expressions for nl = 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, and 5s are obtained. Application to H-like and non-H-like atoms and ions and to neutral atoms demonstrates the universality of the scaled analytical approach including inner-shell photoionization. Likewise, GSPM describes the near-threshold behavior and high-energy asymptotes well. Finally, we discuss the various models and the correspondence principle along with experimental data and with respect to a good compromise between generality and precision. The results are also relevant to large-scale integrated light–matter interaction simulations, e.g., X-ray free-electron laser interactions with matter or photoionization driven by a broadband radiation field such as Planckian radiation.
Highlights
Most of the matter in the universe is ionized and in the so-called plasma state.1–3 There are essentially two main sources of ionization: collisional ionization due to particle impact and photoionization
It is demonstrated that the Thomas–Fermi atom provides surprisingly good overall agreement even for complex outer-shell configurations, where quantum mechanical approaches that include electron correlations are exceedingly difficult
A generalized scaled photoionization model (GSPM) based on the simultaneous introduction of effective charges for non-H-like energies and scaling charges for the reduced energy scale allows the development of analytical formulas for all states nl
Summary
Most of the matter in the universe is ionized and in the so-called plasma state. There are essentially two main sources of ionization: collisional ionization due to particle impact (by electrons, atoms, and ions) and photoionization. Simulation of XFEL interaction with solids requires expressions for photoionization cross-sections from all configurations, including in particular inner atomic shells.. Similar considerations hold true for high-energy-density physics, where intense radiation fields drive important matter ionization: general expressions for the photoionization cross-sections from any configurations of rather complex atoms and ions are required in order to realize large-scale integrated simulations in light–matter interaction physics. It is the aim of the present work to develop various methods that are suitable for general implementation in integrated simulations in which a reasonable compromise between generality and precision can be achieved.
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