An electron-impact-ionization mechanism for ions is considered in which the projectile is first captured by the target to form a doubly excited resonant intermediate state. Subsequently, this state decays in two steps by double Auger emission. The effect upon the ionization cross section is large near the excitation threshold and effectively extends the apparent threshold for scattering excitation single Auger ionization to lower energies. A detailed calculation of the ionization cross section and rate coefficient is presented for ${\mathrm{Fe}}^{15+}$ targets.

• Received 13 April 1981

DOI:https://doi.org/10.1103/PhysRevA.24.2273