Relativistic many-body calculations of transition probabilities for the 2/(1)2/(2)[LSJ]-2/(3)2/(4)[L ' S ' J '] lines in Be-like ions

Reduced matrix elements, oscillator strengths, and transition rates are cal culated for all allowed and forbidden 2s-2p electric dipole transitions in berylliumlike ions with nuclear charges ranging from Z = 4 to 100. Many-bod y perturbation theory (MBPT), including the Breit interaction, is used to e valuate retarded El matrix elements in length and velocity forms. The calcu lations start with a 1s(2) Dirac-Fock potential and include all possible n = 2 configurations, leading to 4 odd-parity and 6 even-parity states. First -order perturbation theory is used to obtain intermediate coupling coeffice nts. Second-order MBPT is used to determine the matrix elements, which are evaluated for the 16 possible El transitions. The transition energies used in the calculation of oscillator strengths and transition rates are evaluat ed using second-order MBPT. The importance of virtual electron-positron pai r (negative energy) contributions to the transition amplitudes is discussed .