Rydberg transitions in Be‐like Si XI

Measurements of Δn=1 Rydberg transition wavelengths for Be‐like Si XI are presented for 1s22s9l’←1s22s10l and 1s22s8l’←1s22s9l. The large polarizability of the open core 1s22s and configuration interaction with nearby 1s22pnl states yield observable 1‐structure that is compared with the polarization model, Multi Configurational Dirac‐Fock (MCDF) and Many Body Perturbation Theory (MBPT) calculations. We discussed the high‐1 structure of the n=9–10 transition previously in relation to plasma observations. The first application of MBPT calculations to Be‐like Rydberg states was reported with our measurement of the 7I–8K transition in S XIII.