Relativistic distorted-wave calculation of electron impact excitation cross sections of be-like N3+ and O4+ ions

By using a fully relativistic distorted-wave method, the electron impact excitation cross sections of Be-like N3+ and O4+ ions from the ground state 2s(21)S to 2s2p (1,3) P, 2p(23)P, D-1 and S-1 2s2p and from the metastable 2s2p P-3 to 2p(23)P have been calculated systematically. Meanwhile, the correlation effects of target states are also discussed. For the low energy collisions the correlation effects play a very important role, and accurate target wavefunctions are needed, but for the high energy collisions, the more correlation effects are not so important. For two-electron excitations, the configuration interactions are very important and the excitations from ground state to the 2p(23)P(0) and S-1(0) have larger cross sections than the other tow electron excitations.