Relativistic and correlation effects in electron impact excitation of forbidden transitions of OII

We investigate relativistic and correlation effects in electron impact excitation of singly ionized oxygen using the Breit-PauliR-matrix method. The intermediate coupling close-coupling calculations are carried out using a 16-level target representation dominated by the electronic configurations 1s22s22p3 ,1 s 22s2p4, 1s22s22p23s. Resonance structures are delineated in detail to ascertain the effect on averaged collision strengths. Convergence of the partial wave summation is ensured for non-dipole transitions in the R-matrix calculations. The present results differ significantly from the similar Breit-Pauli R-matrix calculations by McLaughlin and Bell (1998 J. Phys. B: At. Mol. Opt. Phys. 31 4317-29), but are essentially in agreement with the LS coupling results of Pradhan (1976a J. Phys. B: At. Mol. Opt. Phys. 9 433-43, 1976b Mon. Not. R. Astron. Soc. 177 31-8). A comprehensive study of the detailed energy behaviour of all forbidden transitions among the five levels of the ground configuration, i.e. 2s2p3 4So 3/2, 2Do 5/2,3/2, 2Po 3/2,1/2 shows that the finestructure collision strengths do not significantly depart from the values obtained from a purely LS −→ LSJ transformation, and relativistic effects are therefore small. We find that the Maxwellian-averaged effective collision strengths for the ten transitions also differ from the previous work, most likely due to more extensive delineation of resonances in the present work. However, the differences are largely systematic and therefore the OII line intensity ratios are not significantly affected. We also obtain an excellent agreement between the present-calculated cross sections for the 4So − 2Do transition and the experimental merged beam measurements.