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

Abstract

Experimental cross sections for m-fold photodetachment (m = 3 − 6) of silicon anions via Kshell 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 multiconfiguration 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.

High-precision Transition Energy Measurements of Neon-like Fe xvii Ions

“…The dimensional stability of its electron-optics components is affected by thermal drifts caused by varying ambient conditions at ppm levels to which we are already sensitive. Note that we also fit our data with skewed Voigt profiles, allowing for a nonzero skewness, thus accounting for any line asymmetries that may exist due to monochromator imperfections (Perry-Sassmannshausen et al 2021;Hoesch et al 2022;Togawa et al 2023). These tests resulted in changes to the line centroids of less than ∼1 meV, which is negligible considering the total uncertainty of our measurements.…”

Multiple photodetachment of oxygen anions via K -shell excitation and ionization: Direct double-detachment processes and subsequent deexcitation cascades

“…To establish a hierarchy of useful cascade models, different approaches are distinguished in JAC in order to support and analyze a systematically improved representation of the fine structure and amplitudes. Unlike for Si − ions [30], the rather simple shell structure of O − with just a 1s 2 2s 2 2p 5 ground configuration enables us to apply a self-consistent treatment of all blocks of the cascades (approach B), in addition to just an averaged single-configuration approach (approach A). Indeed, approach A, as the simplest, neglects all configuration mixing between the bound-state levels and also restricts the computations to just a single set of continuum orbitals for each step of the cascade [31].…”