Plots of ion TOF versus arrival <em>X</em> position on the detector before (a) and after (b) compensation of the TOF for seven isotopes of Xe<sup>9 +</sup>

<p><strong>Figure 2.</strong> Plots of ion TOF versus arrival <em>X</em> position on the detector before (a) and after (b) compensation of the TOF for seven isotopes of Xe<sup>9 +</sup>. (c) and (d) show the projections of (a) and (b), respectively. The numbers in (d) indicate the mass of the Xe isotopes in atomic mass units.</p> <p><strong>Abstract</strong></p> <p>We have investigated multiphoton multiple ionization of argon and xenon atoms at 5 keV using a new x-ray free electron laser (XFEL) facility, the SPring-8 Angstrom Compact free electron LAser (SACLA) in Japan. The experimental results are compared with the new theoretical results presented here. The absolute fluence of the XFEL pulse has been determined with the help of the calculations utilizing two-photon processes in the argon atom. The high charge states up to +22 observed for Xe in comparison with the calculations point to the occurrence of sequential <em>L</em>-shell multiphoton absorption and of resonance-enabled x-ray multiple ionization.</p>