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

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 prethreshold resonances associated with the excitation of a 1s electron to higher, either partly occupied or unoccupied atomic subshells. Results from multiconfiguration Dirac-Fock calculations agree with the experimentally derived cross sections for photoabsorption 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.