Relativistic many-body calculations of transition probabilities for the 2l12l2[LSJ]-2l33l4[L´S´J´] lines in Be-like ions

Abstract

Reduced matrix elements, oscillator strengths, and transition rates are calculated for 2l12l2[LSJ]-2l33l4[L´S´J´] electric-dipole transitions in beryllium-like ions with nuclear charges Z from 6 to 100. Many-body perturbation theory (MBPT), including the Breit interaction, is used to evaluate retarded dipole matrix elements in length and velocity forms. The calculations start with a 1s2 Dirac-Fock potential and include all possible n = 2 and n = 3 configurations. We use first-order perturbation theory to obtain intermediate coupling coefficients and second-order MBPT to determine matrix elements. The transition energies used to evaluate transition probabilities are also obtained from second-order MBPT. The importance of negative-energy contributions to the transition amplitudes in maintaining gauge independence is discussed. Our results for 2s3p 1,3P1-2s2 1S0 transitions are compared with available theoretical and experimental data throughout the isoelectronic sequence. Rates for 2l3l´ [J = 1]-2s2 1S0, 2l3l´ [J = 1]-2p2 1S2, 2l3l´ [J = 1]-2s2p 1P1, and 2l3l´ [J = 2]-2s2p 1P1 transitions are given graphically for all Z.