Shake-up processes following K-shell photoionization in the Boron isoelectronic sequence

The direct and conjugate shake-up cross sections for the 2p → 3p, 3s and 2s → 2p, 3s transitions are calculated for CII, NIII, OIV, FV and NeVI in a close-coupling approximation using the R-matrix method. We find that the total shake-up cross section relative to that for single photoionization decreases with increasing Z. The decrease is about a factor 10 when going from BI to NeVI. When the full shake-up regime is reached, i.e. for about twice the 1s threshold energy, the cross section ratio ranges from about 15% for CII to about 3.5% for NeVI, of the single 1s inner-shell photoionization cross section. The 2s → 3s transition gives the dominant contribution for all ions. The 2p → 3p and 2s → 2p excitation contributions are broadly comparable in this energy range, while the 2p → 3s transition is negligible. Our results suggest that the importance of shake off excitation is significant for low Z ions.