Relativistic effects on transition probabilities in the Li and Be isoelectronic sequences

We have evaluated relativistic dipole oscillator line and momentum strengths for a number of elements in the Li and Be isoelectronic sequences. In the Li sequence, the transitions considered are 2s1/2-2p1/2,3/2, 2s1/2-3p1/2,3/2, 2p1/2-3d3/2, and 2p3/2-3d3/2,5/2; in the Be sequence, 2s1/2²-2s1/22p1/2,3/2. The two electromagnetic-field gauges which in the nonrelativistic limit give the length and velocity forms of the transition operator have been used. The heaviest element considered in both sequences was uranium. Relativistic wave functions were obtained using a multiconfiguration Dirac-Hartree-Fock calculation. Nonrelativistic calculations of similar accuracy were also carried out for comparative purposes. The results are discussed with a particular emphasis on how relativistic effects manifest themselves, and under what conditions.