Atomic data from the IRON Project .22. Radiative rates for forbidden transitions within the ground configuration of ions in the carbon and oxygen isoelectronic sequences

As part of the IRON Project, radiative rates have been calculated for the forbidden transitions within the ground configuration of atoms and ions in the carbon (2s(2)2p(2)) and oxygen (2s(2)2p(4)) isoelectronic sequences for Z less than or equal to 28. The atomic structure code SUPERSTRUCTURE was used, which allows for configuration interaction, relativistic effects and semi-empirical term energy corrections. Comparisons are made with previous theoretical datasets for the same sequences. It is shown once again that, to obtain reliable transition probabilities, in particular those of the electric quadrupole type, it is essential to use accurate and consistent experimental transition wavelengths. For the C and O sequences such data are fortunately available from the work of Edlen (1983, 1985). The general accuracy of the present probabilities is rated to be within 10%, with the exception of some electric quadrupole transitions in low-Z ions whose radiative rates are small with an accuracy not better than +/-50%.