Atomic data from the IRON Project. XXXIII. Radiative rates for the intercombination transitions in the carbon isoelectronic sequence

Radiative decay rates are computed with the atomic structure code superstructure for the 2s2psp3 sp5S spo_2 - 2ssp22p sp2 sp3P_1 , sp3P_2 and sp1D_2 intercombination transitions of the carbon isoelectronic sequence (6 <= Z <= 28). Contributions from configuration interaction and relativistic corrections are carefully studied, in particular the spin-spin interaction that is shown to be of considerable importance for low Z. By extensive comparisons with other theoretical datasets and measurements of the sp5S spo_2 radiative lifetime and the B=A(sp5S spo_2 - sp3 P_2)/A(sp5S spo_2 - sp3 P_1) branching ratio, we are able to assign accuracy ratings to the present transition probabilities. The transitions to the ground term are believed to be accurate to better than 10% whereas the smaller A-values belonging to transitions to the sp1 D_2 are not expected to be accurate to more than 20%. A detailed table of the present transition probabilities is available in electronic form from the CDS via anonymous ftp 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html