Proposed resonant mechanisms for producing F <sup>9 +</sup> with intermediate excitation

<p><strong>Figure 4.</strong> Proposed resonant mechanisms for producing F <sup>9 +</sup> with intermediate excitation. Solid vertical arrows: photoionization. Dashed vertical arrows: photoexcitation with excitation energies in brackets. * indicates excited states.</p> <p><strong>Abstract</strong></p> <p>We investigate the multiphoton ionization and the subsequent fragmentation of SF<sub>6</sub> molecules with intense x-ray-free electron laser pulses at different photon energies. We observe highly charged molecular and atomic ions which were absent in previous experiments with conventional x-ray sources. The observation of fully stripped fluorine ions suggests sequential multiphoton ionization processes with intermediate 1s electron excitation. We measure the average momentum and kinetic energy of each fragment, the comparison of which implies many-body fragmentation pathways of the molecular ions. The observed non-monotonic dependence of the kinetic energy on the charge states of fluorine indicates the multiphoton ionization of 'isolated' atomic neutral fluorine or fluorine ions resultant from bond cleavages and also implies the fragmentation of highly charged molecular ions that are produced at a later time during a single pulse.</p>