Resonant compton scattering of two photons by a multiply charged atomic ion

A pronounced $K\alpha_{1,2}$ X-ray emission spectrum is theoretically predicted for the resonant inelastic scattering of two photons in the energy region near the $1s$ shell ionization threshold of a free multiply charged atomic ion. The observed double differential scattering cross section is estimated quantitatively. The results for the Fe$^{16+}$ ion may be important in interpreting the X-ray emission spectra from galactic clusters, active galactic nuclei, and stars.