MULTIPLE IONIZATION OF IRON BY ELECTRON-IMPACT

We have used a pulsed crossed beam technique incorporating time-of-flight spectroscopy of the collision products to study the electron impact ionization of ground state Fe atoms. Relative cross sections sigma(n) for the formation of 1 to 4 times ionized iron have been measured within the energy range 8-1250 eV. Individual cross sections have been obtained by normalization to lower energy values of sigma2 previously measured by Freund et al using a fast crossed beam experiment where analysis was complicated by the presence of metastable atoms in Fe beams. Measured cross sections exhibit evidence of contributions from inner shell electrons. Our high energy values of sigma1 are in excellent agreement with theoretical predictions based on the first Born approximation.