The shape and shift of the resonance lines of Ca+perturbed by electron collisions

The impact theory of Baranger (1958), in which the perturbing particles are treated quantum-mechanically, is clarified and extended to give a general relatively simple expression for the width and shift of an isolated line using an LS coupling scheme to describe the radiating atomic system. For the case of a radiating positive ion this result is shown to be free of explicit dependence on the phase shifts for Coulomb scattering. The width and shift of the resonance lines in Ca + perturbed by electron collisions are then calculated using the scattering data of Burke and Moores, and the results are in reasonable agreement with existing semi-classical estimates. The discrepancy between theory and experiment is partially resolved.