  We demonstrate the correspondence between theoretically calculated K-shell
resonances lying below the K-edge in multiple ionization states of an element
(Pradhan et al. 2009), and recently observed K-alpha resonances in
high-intensity X-ray free-electron laser (XFEL) plasmas (Vinko et al. 2012).
Resonant absorptions in aluminum ions are computed and found to reproduce
experimentally observed features. Results are also presented for titanium for
possible observation of K-alpha resonances in the 4.5-5.0 keV energy range. A
possibly sustainable excitation mechanism for K-alpha resonance fluorescence
might be implemented using two monochromatic X-ray beams tuned to the K-edge
and the K-alpha resonant energies simultaneously. This targeted
ionization/excitation would create inner-shell vacancies via Auger decay, as
well as pump K-alpha resonances. The required X-ray fluence to achieve
resonance fluorescence would evidently be much less than in the XFEL
experiments, and might enable novel biomedical applications.

Atomic and Molecular Clusters;Atomic Physics