ABSTRACT:Oscillator strengths for E2-forbidden spectral lines of sodium-isoelectronic ions, from K IX (Z = 19) to Cs XLV (Z = 55), have been calculated in the LS-coupling scheme using the relativistic quantum defect orbital (RQDO) method. The study of many of these sodiumlike ions is relevant to processes in fusion devices and in astrophysical objects. Our data are compared with the very few results available, and their systematic trend is analyzed for np 2 P 0 -n f 2 F 0 transitions. The influence of relativistic effects in E2 transitions along this sequence is also discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 90: [403][404][405][406][407][408][409] 2002