Multiconfiguration Hartree-Fock results with Breit-Pauli corrections for forbidden transitions in the2p4configuration

Energy levels and fine-structure splittings are calculated for the ground-state configuration of the oxygen isoelectronic sequence using the multiconfiguration Hartree-Fock method with Breit-Pauli corrections. Electric quadrupole and magnetic dipole transition probabilities are reported for transitions between several of these levels. Our results are compared with those from other theories and, in the case of energy levels, also with observation. For degrees of ionization up to about 12 ($Z=20\mathrm{}$), our energy levels are in better agreement with observation than other theories, but for ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$ a relatively larger, systematic discrepancy remains.