Multiple photodetachment of silicon anions via K-shell excitation and ionization

TL;DR

This study measures and models the multiple photodetachment cross sections of silicon anions via K-shell excitation and ionization, providing insights into their behavior under high-energy photon exposure relevant to astrophysical environments.

Contribution

It presents experimental cross sections for silicon anions' multiple photodetachment and compares them with advanced MCDF calculations, including modeling of deexcitation cascades.

Findings

Experimental cross sections match MCDF calculations with small energy shifts.

Deexcitation cascade modeling agrees well for direct K-shell detachment.

Results aid in identifying silicon anions in astrophysical plasmas.

Abstract

Experimental cross sections for $m$-fold photodetachment ($m=3-6$) of silicon anions via $K$-shell excitation and ionization were measured in the photon-energy range of 1830-1900 eV using the photon-ion merged-beams technique at a synchrotron light source. All cross sections exhibit a threshold behavior that is masked by pre-threshold resonances associated with the excitation of a $1s$ electron to higher, either partly occupied or unoccupied atomic subshells. Results from multi-configuration Dirac-Fock (MCDF) calculations agree with the experimentally derived cross sections for photo-absorption if small energy shifts are applied to the calculated resonance positions and detachment thresholds. Moreover, a systematic approach is applied for modeling the deexcitation cascades that set in after the initial creation of a $K$-shell hole. The resulting product charge-state distributions compare well with the measured ones for direct $K$-shell detachment but less well for resonant $K$-shell excitation. The present results are potentially useful for identifying silicon anions in cold plasmas such as interstellar gas clouds.