Abstract
Cross sections for optically allowed transitions in positive ions, produced by electron impact, have contributions from an inner region for which the colliding electron penetrates the target, and from an outer region for which it does not. The contributions from the outer region converge rather slowly but can be summed using a method due to Burgess (1974) based on the Coulomb-Bethe approximation. A discussion is given on the use of the method in conjunction with close-coupling calculations. Results are presented for three transitions in C2+ using close coupling both with and without exchange.

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