Near K-Edge Photoionization and Photoabsorption of Singly, Doubly, and Triply Charged Silicon Ions

TL;DR

This paper combines experimental and theoretical approaches to study K-shell photoionization of silicon ions, providing detailed resonance data and improved cross sections relevant for astrophysical observations.

Contribution

It presents new high-resolution experimental data and advanced theoretical calculations for silicon ion photoionization, enhancing accuracy over previous models.

Findings

Resonance energies, widths, and strengths were precisely measured.

Theoretical cross sections agree better with experiments than earlier results.

Results aid in distinguishing silicon absorption in interstellar medium.

Abstract

Experimental and theoretical results are presented for double, triple, and quadruple photoionization of Si$^+$ and Si$^{2+}$ ions and for double photoionization of Si$^{3+}$ ions by a single photon. The experiments employed the photon-ion merged-beams technique at a synchrotron light source. The experimental photon-energy range 1835--1900 eV comprises resonances associated with the excitation of a $1s$ electron to higher subshells and subsequent autoionization. Energies, widths, and strengths of these resonances are extracted from high-resolution photoionization measurements, and the core-hole lifetime of K-shell ionized neutral silicon is inferred. In addition, theoretical cross sections for photoabsorption and multiple photoionization were obtained from large-scale Multi-Configuration Dirac-Hartree-Fock (MCDHF) calculations. The present calculations agree with the experiment much better than previously published theoretical results. The importance of an accurate energy calibration of laboratory data is pointed out. The present benchmark results are particularly useful for discriminating between silicon absorption in the gaseous and in the solid component (dust grains) of the interstellar medium.