Photoionization of metastable heliumlike C4+(1s 2s 3S1) ions: Precision study of intermediate doubly excited states

TL;DR

This study combines high-resolution experiments and advanced theory to precisely investigate intermediate doubly excited states in the photoionization of metastable heliumlike C4+ ions, improving energy standards at synchrotron facilities.

Contribution

It provides highly accurate measurements and calculations of resonance energies and cross sections for doubly excited states in heliumlike C4+ ions, enhancing understanding of their photoionization processes.

Findings

Resonance energies with uncertainties below ±1 meV.

High-resolution measurements with resolving power up to 25,000.

Theoretical calculations agree with experimental results, confirming their reliability.

Abstract

In a joint experimental and theoretical endeavour, photoionization of metastable C4+(1s 2s 3S1) ions via intermediate levels with hollow, double-K-vacancy configurations 2s2p, 2s3p, 2p3s, 2p3d, 2s4p, 2p4s and 2p4d has been investigated. High-resolution photon-ion merged-beams measurements were carried out with the resolving power reaching up to 25,000 which is sufficient to separate the leading fine-structure components of the 2s2p 3P term. Many-body perturbation theory was employed to determine level-to-level cross sections for K-shell excitation with subsequent autoionization. The resonance energies were calculated with inclusion of electron correlation and radiative contributions. Their uncertainties are estimated to be below $\pm$1 meV. Detailed balance confirms the present photoionization cross-section results by comparison with previous dielectronic-recombination measurements. The high accuracy of the theoretical transition energies together with the present experimental results qualify photoabsorption resonances in heliumlike ions as new, greatly improved energy-reference standards at synchrotron radiation facilities.