CORRELATION AND NEGATIVE CONTINUUM EFFECTS FOR THE RELATIVISTIC M1 TRANSITION IN 2-ELECTRON IONS USING THE MULTICONFIGURATION DIRAC-FOCK METHOD

The role of the E < -mc(2) continuum and of correlation in the multico nfiguration Dirac-Fock calculation of nondiagonal one-electron operato rs is describe;l. Because df its importance and symmetry which emphasi ze both effects, we study the 1s2s S-3(1) --> 1s(2) S-1(0) relativisti c M1 transition in two-electron ions. It is shown that both contributi ons have the same magnitude, and must be included even at low Z. These contributions improve significantly the agreement:between theory and experiment at all Z, reducing the disagreement for Nb from 2.7 to -1.8 times the experimental error.