Inner-shell photodetachment from a Si⁻ negative ion: strong effect of many-electron correlations

The first theoretical investigation of the inner-shell single-photodetachment from the Si⁻ (1s²2s²2p⁶3s²3p³⁴S^o) negative ion is presented. The partial and total cross sections, the photoelectron phase shifts, and the parameters of angular anisotropy are calculated in the framework of the many-body theory for L-shell photodetachment from Si⁻ ion in the experimentally accessible range of photon energies (7.5–14 Ry ). Comparison is made between the calculations of the response of the ionic many-electron system Si⁻ to an electromagnetic field at the different levels of approximation: the 'frozen-field' random phase approximation with exchange (RPAE), and the static relaxation approximation. The optimal analysis is made when the dynamic relaxation and polarization are included within the Dyson equation method (DEM) simultaneously with the RPAE corrections (the RPAE and DEM approach). It is predicted that the photoexcitation to a resonance state of complex 'shape-Feschbach' nature in the open p-shell reveals itself as a prominent resonance structure in the photodetachment cross sections in the energy range of the 2s and 2p inner shell thresholds similar to that in 1s inner-shell photodetachment from C⁻ (2006 J. Phys. B: At. Mol. Opt. Phys. 39 1379). The photodetachment dynamical characteristics clearly demonstrate the significance of all the considered many-electron correlations within the RPAE and DEM approach, however the total photodetachment cross section is dominated by a strong resonance peak just after the 2s threshold. Dynamical relaxation (screening) is identified as a decisive factor in the formation of this resonance. (paper)