Forbidden transitions in B II, C III, O V, Ne VII and Mg IX

Intercombination line transition rates between n=2 levels of B II, O V, Ne VII and Mg IX have been calculated using the configuration interaction code CIV3. The recommended A-values for the 2s2p P-3(1)o-2s(21)S(0) intercombination lines are 9.73 s(-1) for B II, 2280 s(-1) for O V, 19 204 s(-1) for Ne VII and 97 242 s(-1) for Mg IX. We estimate that the accuracy of these values is better than 2 per cent. Calculations of the M2, E2 and M1 transitions have also been carried out for these ions and for C III.