Published online by Cambridge University Press: 14 August 2015
New calculations of collision strengths are being made for ions in configurations npq, n = 2 and 3 and q = 1–5. Wave functions for the entire system are represented by sums over anti-symmetrized products of ion functions and orbitals for the colliding electron, and sets of coupled integro-differential equations are obtained for the colliding electron radial functions. The main approximation is neglect of coupling to configurations other than npq. Calculations are made using improved forms of the exact resonance and distorted wave approximations. For the 2pq ions it is found that the dominant contributions come from the p-waves; the exact resonance approximation is used for the p-waves and the distorted wave approximation is used for all other partial waves. It is considered that the results obtained should approximate closely to those which would be obtained from full solutions of the coupled equations. For the 3pq ions the dominant contributions come from the p-waves; for these ions the distorted wave approximation is used for all partial waves.