Electron impact excitation cross sections of Ca+at low energies

A series of different Coulomb distorted-wave (CDW) approximations have been used to evaluate the cross section of Ca + for excitation by electron impact at low energies. The problem has been formulated in the LS coupling scheme, with the target ion being represented by a core plus atomic electron (frozen-core approximation) and exchange between the atomic and the incident electron being neglected. For a given number of states the best of the CDW approximations used gives results which are in very good agreement with the close-coupling calculations, with a significant reduction in the computing time required.