Electron impact excitation of the resonance lines of Be⁺, Mg⁺and Ca⁺

The unitarised distorted-wave polarised-orbital (UDWPO) approximation is used to calculate integral cross sections for electron impact excitation of the resonance transitions of Be + , Mg + and Ca + from threshold to 100 eV. Results are also given in a variety of simpler approximations and the cross sections are compared with other calculations and with experiment. The polarisation of the emitted Ca + K-line radiation is also considered and adiabatic dipole polarisabilities are calculated for the ground states of the above ions.