Calculations of Rydberg energy levels for Ni XVIII using the weakest bound elect

Martin expression about the quantum defect of single-valence atoms is extended to many-valence atoms by identifying the weakest bound electron (WBE) under the weakest bound electron potential model (WBEPM) theory. Six Rydberg series energy levels of 2p6np2Po_(1/2) (n>3), 2p6np2Po_(3/2) (n>3),