Distorted-wave calculations of the electron-impact excitation- autoionization processed from the ground state of highly ionized Ga i like ions through n=1 inner-shell excitations

A systematic investigation of ionization enhancement due to collisional excitation followed by autoionization (EA) is presented for Ga i like rare-earth elements. Both nuclear charge and temperature dependence are analyzed and compared with direct-impact ionization (DI) rates. Collisional excitation and autoionization rates were calculated in the distorted-wave factorization- interpolation method. DI rates were calculated by a modified plane-wave Born approximation method. The rates for the combined EA process for selected Ga i like ions from Mo xii to Dy xxxvi are presented for the relevant temperature ranges. It is shown that indirect ionization is dominant for Mo through Pr but is reduced gradually with Z and approaches zero at Dy. A density diagnosis is provided by the opening of EA channels that are not active at low densities.