Atomic data from the iron project - LV. Electron impact excitation of NiII

We study the effects of using a (4d) over bar pseudo-orbital on the collision strengths for electron impact excitations of forbidden transitions in NiII computed in the close coupling approximation. It is found that the resonance structures of the collision strengths are quite sensitive to the way the pseudo-orbital is created. Further, the close coupling expansion with a single (4d) over bar orbital does not converge, resulting in a poor representation of (N + 1)-electrons auto-ionizing states. Much greater expansions are needed to properly represent resonance structures in electron impact excitation calculations, resulting in variations of up to factors of two, with respect to previous computations, in the Maxwellian averaged excitation rate coefficients.