Electron impact single ionization of multiply charged iron ions

Employing the animated crossed-beams technique, absolute cross sections for electron impact single ionization of the iron isonuclear sequence are meas ured for charge states q = 1-6 for electron energies from threshold up to I keV, as well as for the intermediate charge states q = 9, 10 up to an elec tron energy of 5 keV. The cross sections observed for Feq+ ions in charge s tates q = 1-4, 9 and 10 show a significant ionization signal below the resp ective ground state threshold resulting from ions in excited, long-lived me tastable states in the parent ion beam. In the case of Fe5+ and Fe6+ no met astable components are found. The experimental results are in good agreemen t with the theoretical predictions if excitation-autoionization processes a re taken into account. Our measured cross sections are also in good agreeme nt with experimental results of other groups.