# Single-photon photoionization of oxygen-like Ne III

## TL;DR

This study combines high-resolution experimental measurements and advanced relativistic calculations to analyze the photoionization cross sections of Ne III, revealing prominent resonances and benchmarking theoretical models.

## Contribution

It provides the first detailed benchmark of experimental and theoretical photoionization cross sections for Ne III using a large relativistic close-coupling approach.

## Key findings

- Identification of prominent low-energy resonances near ionization thresholds.
- Observation of high-peak narrow resonances with relativistic effects.
- Good agreement between experimental data and relativistic Breit-Pauli R-matrix calculations.

## Abstract

We offer a theoretical and experimental study of the single-photon photoionization of Ne III. The high photon flux and the high-resolution capabilities of the Advanced Light Source at the LBNL were employed to measure absolute photoionization cross sections. The resulting spectrum has been benchmarked against high accuracy relativistic Breit-Pauli $R$-matrix calculations. A large close-coupling wave function expansion which comprises up to 58 fine-structure levels of the residual ion Ne IV of configurations $2s^22p^3$, $2s2p^4$, $2p^5$, $2s^22p^23s$, $2s^22p^23p$ and $2s^22p^23d$ was included. A complete identification of the measured features was achieved by considering seven low-lying levels of Ne III. We found that the photoionization cross-section ($\sigma_{PI}$) exhibits the presence of prominent resonances in the low-energy region near the ionization thresholds that correspond to low-lying levels. These include high-peak narrow resonances with almost zero background introduced by relativistic effects. However, there does not exist a significant contribution to $\sigma_{PI}$ from relativistic effects at the high-energy interval of the present study.