Perturbers of the silicon (3s)2(3p)1(md)11Do Rydberg series - importance of the spin-orbit interaction

The Si 3s23p1md11D2o Rydberg series is investigated. Experimentally, the series has a large constant quantum defect (QD) up to 3s23p16d1, which increases abruptly there after. Experimentalists consider that the increase in QD is brought about by a perturber 3s13p3. We show that 3s13p3 works as a strong perturber, giving a large and constant QD for the lower members of the series (m ⩽ 6), but does not contribute to the abrupt observed increase in QD. It is found that 3s23p1md13F2o acts as a perturber for the higher member of the 1D2o series through spin-orbit interaction, giving a sharp increase of QD.