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

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Abstract
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 x i i to Dy x x x v i 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.